Tumors of the skin can either be benign (non-cancerous) or malignant (cancerous). There are certain tumors that are classified as atypical (uncertain or unspecified behavior) meaning that some behave in a benign manner, or some behave in a malignant manner. A majority of the skin tumors diagnosed via lab studies (biopsy) are benign.

The World Health Organization (WHO) is an authoritative body that compiles, prepares, and publishes histological and molecular classification of tumors, via their Blue Books, based on research inputs from experts worldwide. These reference books chiefly aid in global cancer research, provide gold standards for tumor diagnosis, and help in treating cancer patients.

According to the WHO Classification of Skin Tumors (2018), 4th Ed., Vol. 11, benign and malignant tumors of skin are classified in the following manner:

Keratinocytic/epidermal tumors:

Carcinomas

• Basal cell carcinoma: It is a malignancy affecting the skin. It is a slow-growing tumor that is generally observed in older adults
  • Nodular basal cell carcinoma: It is the most common type of basal cell carcinoma that is present as a nodule on skin, usually in the head and neck area. It generally affects elderly adults
  • Superficial basal cell carcinoma: It is the most common type of basal cell carcinoma that is present as an erythematous (red) patch on skin of the chest and back. It generally affects elderly adults
  • Micronodular basal cell carcinoma: It is an uncommon type of basal cell carcinoma that is present as a nodule on the skin, usually in the back. It generally affects elderly adults
  • Infiltrating basal cell carcinoma: It occurs as an irregular plaque with a tendency to infiltrate deep into the body tissue, making it difficult to treat. It generally affects elderly adults
  • Sclerosing/morphoeic basal cell carcinoma
  • Basosquamous carcinoma: It is an uncommon, but very aggressive type of basal cell carcinoma that generally affects elderly adults
  • Pigmented basal cell carcinoma
  • Basal cell carcinoma with sarcomatoid differentiation
  • Basal cell carcinoma with adnexal differentiation: It is an uncommon type of basal cell carcinoma that generally affects elderly adults
  • Fibroepithelial basal cell carcinoma: It is an uncommon type of basal cell carcinoma that is present as a solitary reddish nodule on the skin, usually in the back. It generally affects elderly adults
• Squamous cell carcinoma
  • Squamous cell carcinoma: It may appear as slow-growing skin lesions, commonly on the sun-exposed areas, such as the face, neck, hands, and chest. It most commonly affects elderly men and women
  • Keratoacanthoma: It is a tumor of the skin (hair follicles) of low-grade malignancy that typically affects elderly men and women
  • Acantholytic squamous cell carcinoma: It is a common malignant tumor of skin that typically affects elderly men and women
  • Spindle cell squamous cell carcinoma: It is a malignant tumor of skin that is typically seen with a higher frequency in immunosuppressed individuals
  • Verrucous squamous cell carcinoma: It is a malignant tumor of skin that typically affects elderly men and women. It has a lower malignancy potential than conventional squamous cell carcinomas
  • Adenosquamous carcinoma: It is a malignant tumor of skin that typically affects elderly men and women. It is a rare subtype of squamous cell carcinoma of skin and is generally more aggressive than conventional SCCs
  • Clear cell squamous cell carcinoma
  • Other (uncommon) variants
• Squamous cell carcinoma in situ (Bowen disease)
• Merkel cell carcinoma: It is a rare cancer of the skin that usually occurs in elderly individuals. Sun exposure and immunodeficiency are key risk factors for the condition

Carcinoma precursors and benign simulants

• Premalignant keratoses
  • Actinic keratosis: It develops from prolonged exposure to the sun’s ultraviolet rays, resulting in skin DNA damage causing patches of rough, scaly, and thickened skin. The condition is mostly observed in adults over 50 years of age or more
  • Arsenical keratosis: It develops from prolonged exposure of the body to arsenic, leading to damage of the DNA, causing skin signs and symptoms . The condition is mostly observed in adults
  • PUVA keratosis: It is a skin condition that occurs only in patients who are being treated with PUVA therapy. This condition may develop in both children and adults
• Verrucae
  • Verruca vulgaris: It is a very common benign skin infection that is caused by human papilloma virus (HPV). It is frequently seen in children or young adults
  • Verruca plantaris: It is a common benign skin infection that is caused by human papilloma virus (HPV). It is frequently seen in adolescents and young adults
  • Verruca plana: It is a common benign skin infection that is caused by human papilloma virus (HPV). It is frequently seen in children or young adults
• Benign acanthomas/keratoses
  • Seborrheic keratosis: It is one of the most common non-cancerous skin growths in adults. It is characterized by either a brown, black, or pale growth appearing on the chest, face, shoulders or back
  • Solar lentigo: It is a benign tumor of skin that chiefly forms on the sun-exposed areas of the body. It may occur in a wide age range of individuals
  • Lichen planus-like keratosis: It is a common benign skin tumor. It can resemble other benign and malignant tumors such as basal cell carcinoma, seborrheic keratosis, and actinic keratosis, and is commonly seen in adults
  • Clear cell acanthoma: It is a relatively common, benign slow-growing tumor of the skin. the tumor is typically seen in individuals over 40 years of age
  • Large cell acanthoma: It is a rare benign tumor of the sebaceous gland on skin. It is commonly seen in middle-aged and older adults
  • Warty dyskeratoma: It is a rare benign skin tumor that usually occurs in adults, on the head and neck area. It is usually seen in middle-age and older adults
  • Other benign keratoses

Melanocytic tumors:

• Melanocytic tumor classification and the pathway concept of melanoma pathogenesis
• Genomic landscape of melanoma

Melanocytic tumors in intermittently sun-exposed skin

• Low-CSD melanoma (superficial spreading melanoma): It is the most common subtype of cutaneous melanoma that usually arises from the non-exposed skin areas. It can occur in young and old adults
• Simple lentigo and lentiginous melanocytic nevus: It is described as an early phase in the formation of melanocytic nevus. It is a benign, pigmented skin tumor that chiefly forms on the upper and lower limbs. The condition may occur in a wide age range of individuals
• Junctional, compound, and dermal nevi
• Dysplastic nevus: It is an atypical mole/nevus with abnormal shape, borders, or color. While most nevi never become cancerous, a small number of Dysplastic Moles may turn cancerous to melanoma. It may be seen in both children and adults
• Nevus spilus: It is a fairly common condition, wherein there is a potentially large area of pigmented skin patches on the body. It may be present at birth or form at any age
• Special-site nevi (of the breast, axilla, scalp, and ear)
• Halo nevus: It is a benign melanocytic proliferation that show a halo of skin depigmentation around an existing nevus (usually indicating that the mole is under regression). Children and young adults may have this type of nevus
• Meyerson nevus: It is a benign mole of melanocytic cells that occur on the skin surrounded by a halo. The mole causes an eczema-like reaction around it. The nevus may be present in both children and adults
• Recurrent nevus
• Deep penetrating nevus and melanocytoma: It is an uncommon, benign mole that occurs as a deeply-pigmented skin lesion. It is generally noticed between the period of 10 and 30 years
• Pigmented epithelioid melanocytoma
• Combined nevus, including combined BAP1-inactivated nevus / melanocytoma: It is a benign mole that shows histological components of two or more melanocytic moles. This pigmented skin lesion can be either acquired (at any age) or be congenital in nature

Melanocytic tumors in chronically sun-exposed skin

• Lentigo maligna melanoma: It is a type of skin cancer, wherein skin invasion by the melanocytes is observed against a background of lentigo maligna. It can occur in young as well as old individuals
• Desmoplastic melanoma: It is an uncommon subtype of cutaneous melanoma that usually arises from sun-exposed skin sites. It is seen in young and old adults

Spitz tumors

• Malignant Spitz tumor (Spitz melanoma)
• Spitz nevus: It is an uncommon, benign condition that occurs as a pigmented skin lesion. The lesion is usually a well-defined nodule. It is generally noticed before age 40 years
• Pigmented spindle cell nevus (Reed nevus): It is a benign, darkly-pigmented skin lesion that chiefly forms on the upper and lower limbs. Both children and adults may be affected

Melanocytic tumors in acral skin

• Acral melanoma
• Acral nevus: It is a benign condition that occurs as a pigmented skin lesion on the palms or soles. The lesion is generally noticed in individuals between 10 and 30 years old

Genital and mucosal melanocytic tumors

• Mucosal melanomas (genital, oral, sinonasal): They develop from the mucous membrane lining the respiratory, gastrointestinal, or genitourinary tract. These melanoma types are rare and seen in older adults
• Genital nevus: It is a benign condition that occurs as a pigmented skin lesion on the genitalia and in the region between the anus and the genitals. The condition is generally seen in adult men and women

Melanocytic tumors arising in blue nevus

• Melanoma arising in blue nevus: It is a very uncommon condition that is mostly observed in adults. The probability of a cellular blue nevus transforming into a malignant melanoma is greater than melanoma arising from a common blue nevus
• Blue nevus and cellular blue nevus
  • A blue nevus is a benign proliferation of melanocytes in the dermis or skin. It is typically an acquired condition. Children and adolescents are generally noted to have this type of nevus
  • Since the number of melanoma sites is much higher than a regular blue nevus, it is called a cellular blue nevus. It is an unusual type of mole that in rare cases, can turn into a malignant melanoma. Children and adolescents are generally observed to have this nevus type
• Mongolian spot: It is a benign condition where there is increased pigmentation of skin affecting the lower back and buttocks. It is usually present at birth in newborn children
• Nevus of Ito and nevus of Ota: It is a benign skin condition with hyperpigmentation that is found on the head and neck region, mostly in the eye. It is normally present at birth, but may occur in adolescence too

Melanocytic tumors arising in congenital nevi

• Melanoma arising in giant congenital nevus: It is a rare form of melanoma that is mostly seen in children. It arises from the skin component of a giant congenital nevus, which may be described as a very large birthmark
• Congenital melanocytic nevus: It is a common melanocytic mole that is present at birth or develop immediately following birth. It may be present anywhere on the body
• Proliferative nodules in congenital melanocytic nevus

Ocular melanocytic tumors

• Uveal melanoma: These develop when melanomas form from melanocytes in the eye. In adults, this is the most common primary cancer of the eye. The condition can occur in any age group
• Conjunctival melanoma
• Conjunctival melanocytic intraepithelial neoplasia/primary acquired melanosis
• Conjunctival nevus

Nodular, nevoid, and metastatic melanomas

• Nodular melanoma: It is the second-most common subtype of cutaneous melanoma that typically arises from the head and neck region. It is the most aggressive form of melanoma of skin that is mostly observed in older adults
• Nevoid melanoma: It is an uncommon subtype of cutaneous melanoma. The tumor is generally seen in young and middle-aged adults
• Metastatic melanoma: It is described as a melanoma that has spread to areas besides the skin. The primary site of origin could be the skin/mucous membrane/eye. The condition can occur in any individual who had had a primary melanoma

Appendageal tumors:

Malignant tumors with apocrine and eccrine differentiation

• Adnexal adenocarcinoma not otherwise specified
• Microcystic adnexal carcinoma: It is an uncommon malignant tumor of eccrine sweat glands. The tumor normally occurs on the face. It can affect a wide age range of individuals
• Porocarcinoma: It is a rare malignant tumor that originates from the eccrine or apocrine sweat glands. The tumor normally occurs on the lower limbs or head and neck region. The condition is more common in elderly adults
• Malignant neoplasms arising from spiradenoma, cylindroma, or spiradenocylindroma
• Malignant mixed tumor: It is a very rare and highly-aggressive malignancy of the sweat glands. It is frequently known to metastasize. The tumor may be seen in a wide range of individuals, including children and adults
• Hidradenocarcinoma: It is a malignant tumor that may occur spontaneously or arise from a benign hidradenoma. It is observed in adults of a wide age range
• Mucinous carcinoma: It is a very rare, malignant tumor of skin. It is typically observed in middle-aged and older adults. The tumor is normally painless and can develop anywhere on the body
• Endocrine mucin-producing sweat gland carcinoma
• Digital papillary adenocarcinoma
• Adenoid cystic carcinoma: It is a very rare and unusual form of cancer. It is typically observed in middle-aged and older adults and most of the cases are observed in the head and neck region
• Apocrine carcinoma: It is a rare malignancy that originates from the apocrine sweat glands. The tumor normally occurs on the armpits. It is more common in adults than children
• Squamoid eccrine ductal carcinoma
• Syringocystadenocarcinoma papilliferum
• Secretory carcinoma
• Cribriform carcinoma
• Signet-ring cell/histiocytoid carcinoma

Benign tumors with apocrine and eccrine differentiation

• Hidrocystoma/cystadenoma
• Syringoma: It is a benign tumor of the eccrine (sweat) glands of skin. It develops on skin as a painless papule, usually in young adults
• Poroma: It is a common, benign tumor of the sweat glands. It can arise either from the apocrine or eccrine sweat gland, and is seen in a wide age range of adults
• Syringofibroadenoma: It is a slow-growing and usually solitary tumor that occurs as a painless nodule on skin. It is seen in older adults and is typically present on the arms or legs
• Hidradenoma: It is a slow-growing and usually solitary tumor that occurs as a painless nodule. The tumor is often seen in young to older adults
• Spiradenoma
• Cylindroma: It is a benign tumor of skin that may occur as a papule or nodule. It is a slow-growing and usually solitary tumor that is seen in middle-aged and older adults
• Tubular adenoma
• Syringocystadenoma papilliferum: It is a rare condition in which a tumor occurs in the apocrine sweat glands. It can be present at birth or observed in young children
• Mixed tumor
• Myoepithelioma

Malignant tumors with follicular differentiation

• Pilomatrical carcinoma
• Proliferating trichilemmal tumor
• Trichoblastic carcinoma/carcinosarcoma
• Trichilemmal carcinoma

Benign tumors with follicular differentiation

• Trichoblastoma: It is a benign tumor of the hair follicles on skin. The tumor is usually solitary and can be present in individuals of all age groups
• Pilomatricoma: It is a benign and generally slow-growing skin tumor of the hair follicle. It is common and usually found in the head and neck region. It can occur in both children and adults
• Trichilemmoma: It is a benign, slow-growing tumor of the hair follicles on skin. It is typically observed in adults
• Trichofolliculoma: It is a rare and benign tumor of the hair follicles on skin. It can occur in children and young adults
• Pilar sheath acanthoma: It is a benign tumor of the hair follicles, usually seen on the face. It is an uncommon skin condition that typically occurs in middle-aged and older adults
• Tumor of the follicular infundibulum: It is a benign, slow-growing tumor of the hair follicles. It is common in middle-age and older age
• Melanocytic matricoma
• Spindle cell–predominant trichodiscoma

Tumors with sebaceous differentiation

• Sebaceous carcinoma: It is a very rare, malignant tumor of skin, most frequently seen on the eyelids. The malignancy is usually seen in adults
• Sebaceous adenoma: It is a benign tumor of the sebaceous gland occurring on skin. These are painless, slow-growing tumors that occur in young adulthood to middle-age
• Sebaceoma: It is a rare, benign tumor of the sebaceous gland occurring on skin. The tumor may be associated with Muir-Torre syndrome, a genetic condition causing cancers in various parts of the body

Site-specific tumors

• Mammary Paget disease: Paget’s Disease of the Breast is a rare form of breast cancer that starts from the nipple and extends to the areola around the nipple. It is most commonly seen in women over 50 years’ of age
• Extramammary Paget disease
• Adenocarcinoma of anogenital mammary-like glands
• Hidradenoma papilliferum: It is a slow-growing and usually solitary tumor that occurs as a painless nodule. It is often seen in middle-aged women
• Fibroadenoma and phyllodes tumor of anogenital mammary-like glands

Tumors of hematopoietic and lymphoid origin:

• Mycosis fungoides: It is a cutaneous T-cell non-Hodgkin’s lymphoma. In the beginning stage, it is a low-grade malignancy and as the tumor progresses, it can become highly-aggressive. The condition may be seen in both children and adults

Variants of mycosis fungoides

• Folliculotropic mycosis fungoides: It is a rare variant of Mycosis Fungoides, which is a cutaneous T-cell non-Hodgkin’s lymphoma. Here, the malignant lymphocytes involve the hair follicles. The condition generally affects adults of a wide age group
• Granulomatous slack skin: It is a type of primary cutaneous T-cell non-Hodgkin’s lymphoma. The lymphoma first originates in the skin and later involve other parts of the body. The condition generally affects adults of a wide age group
• Pagetoid reticulosis: It is a variant of Mycosis Fungoides, which is a cutaneous T-cell non-Hodgkin’s lymphoma. It is usually present as a single, slow-growing patch on the arm or leg. The condition generally affects adults of a wide age group
• Sezary syndrome: It is a rare, aggressive form of T-cell non-Hodgkin’s lymphoma that can affect the skin. It generally occurs in adults over the age of 50 years

Primary cutaneous CD30+ T-cell lymphoproliferative disorders

• Lymphomatoid papulosis: It is a rare cutaneous T-cell non-Hodgkin’s lymphoma and is considered to be CD-30 positive T-cell lymphoproliferative disorder. The condition generally affects adults
• Primary cutaneous anaplastic large cell lymphoma: It is a primary cutaneous T-cell non-Hodgkin’s lymphoma. It is the second most common skin T-cell lymphoma after mycosis fungoides. The condition generally affects adults
• Cutaneous adult T-cell leukemia/lymphoma
• Subcutaneous panniculitis-like T-cell lymphoma: It is a rare type of primary cutaneous T-cell non-Hodgkin’s lymphoma. It is characterized by the presence of multiple subcutaneous nodules all over the body
• Cutaneous manifestations of chronic active EBV infection
• Extranodal NK/T-cell lymphoma, nasal type: It is a rare type of ‘extranodal lymphoma’ that usually develops in the nose, nasal passage, and paranasal sinuses. It is most common in adults over the age of 50 years

Primary cutaneous peripheral T-cell lymphomas, rare subtypes

• Primary cutaneous gamma-delta T-cell lymphoma: It is a primary cutaneous T-cell non-Hodgkin’s lymphoma. The condition is a very rare and aggressive form of T-cell lymphoma, generally affecting adults
• Primary cutaneous CD8+ aggressive epidermotropic cytotoxic T-cell lymphoma: It is an aggressive primary cutaneous T-cell non-Hodgkin’s lymphoma. It is a very rare form of T-cell lymphoma that generally affects adults
• Primary cutaneous acral CD8+ T-cell lymphoma: It is a primary cutaneous T-cell non-Hodgkin’s lymphoma. It is a rare and less aggressive form of T-cell lymphoma that generally affects middle-aged adults
• Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder

Secondary cutaneous involvement in T-cell lymphomas and leukemias

• Systemic anaplastic large cell lymphoma
• Angioimmunoblastic T-cell lymphoma: It is a common condition that takes place secondary to systemic disease, meaning that the disease affects other body organs first, before affecting the skin. Middle-aged and older adults have the highest risk for this form of lymphoma
• T-cell prolymphocytic leukemia
• Primary cutaneous marginal zone (MALT) lymphoma: It is a rare, cutaneous B-cell non-Hodgkin’s lymphoma. It is a slow-growing tumor that affects middle-aged and older adults
• Primary cutaneous follicle center lymphoma
• Primary cutaneous diffuse large B-cell lymphoma, leg type: It is a cutaneous B-cell non-Hodgkin’s lymphoma, generally affecting the skin of the leg. It is a type of diffuse large B-cell lymphoma, generally seen in older adults
• Intravascular large B-cell lymphoma: It is a cutaneous B-cell non-Hodgkin’s lymphoma. The condition generally affects middle-aged and older adults
• EBV-positive mucocutaneous ulcer
• Lymphomatoid granulomatosis: It is a rare, cutaneous B-cell non-Hodgkin’s lymphoma. It is difficult to find primary cutaneous Lymphomatoid Granulomatosis. The condition generally affects adults

Cutaneous involvement in primarily extracutaneous B-cell lymphomas and leukemias

• Mantle cell lymphoma: It is rare and takes place secondary to systemic disease, meaning that the disease affects other body organs first, before affecting the skin. This lymphoma type is generally found in older adults
• Burkitt lymphoma: It is very rare and takes place secondary to systemic disease, meaning that the disease affects other body organs first, before affecting the skin. This lymphoma type is generally noted in children and young adults
• Chronic lymphocytic leukemia/small lymphocytic lymphoma
• T-lymphoblastic and B-lymphoblastic leukemia/lymphoma
• Blastic plasmacytoid dendritic cell neoplasm
• Cutaneous involvement in myeloid leukemia
• Cutaneous mastocytosis: It is the most common form of mastocytosis affecting the skin. In this type, there is an increase in mast cells in skin. the condition is mostly observed in children

Introduction to histiocytic and dendritic cell neoplasms

• Langerhans cell histiocytosis: It is a rare, complicated, and non-heritable genetic disorder that can result in tumor formation in many different body parts. The disorder typically affects very young children
• Indeterminate cell histiocytosis/indeterminate dendritic cell tumor: It is a very rare skin disorder wherein an overgrowth and accumulation of certain cells, called indeterminate cells, is observed in skin. The condition seen in both children and adults
• Rosai-Dorfman disease: Cutaneous Rosai-Dorfman Disease is a form of extranodal RDD, when only the skin is involved, and involvement of the lymph nodes is typically absent. The affected individuals are generally 45 years or older
• Juvenile xanthogranuloma: It is a rare benign condition affecting young children. It is characterized by the formation of papules and nodules involving the skin, and rarely, the eye
• Erdheim–Chester disease: Erdheim–Chester disease is a highly infrequent disorder affecting multiple body systems, due to excess production and collection of histiocytic cells in the tissues and organs. Adults in the age group of 50-70 years are affected the most
• Reticulohistiocytosis

Soft tissue tumors:

Adipocytic tumors

• Atypical lipomatous tumor
• Pleomorphic liposarcoma: It is a very rare and aggressive type of sarcoma that is typically present on the lower limbs. The malignancy is observed with a slightly higher incidence in men
• Lipoma: It is a very common benign tumors of fat tissues (adipose tissues). Lipomas are usually observed in middle-aged and older adults
• Spindle cell/pleomorphic lipoma
• Angiolipoma: It is a kind of benign tumor that has a combination of benign fatty tissue and benign blood vessels. These tumors are usually found in young adults
• Nevus lipomatosus superficialis

Fibroblastic, myofibroblastic, and fibrohistiocytic tumors

• Myxoinflammatory fibroblastic sarcoma: It is a rare and malignant soft tissue tumor that is found to be locally aggressive. In a majority of cases, this sarcoma type is found in middle-aged adults
• Dermatofibrosarcoma protuberans and variants: It is a rare tumor of the subcutaneous tissue of skin. These tumors occur as masses on the skin, commonly in young to middle-aged adults
• Plexiform fibrohistiocytic tumor: It is a rare, low-to-intermediate grade, soft tissue tumor occurring on skin, or just below the skin. The tumor is generally present in young girls and women
• Superficial fibromatosis
• Dermatofibroma (fibrous histiocytoma) and variants: It is a benign tumor that develops from proliferation of a specific type of cells, called histiocytes, in the body. It is a common tumor that occurs on the skin as a painless nodule. It can occur at any age
• Epithelioid fibrous histiocytoma
• Fibromas
  • Fibroma of tendon sheath: It is a benign, uncommon tumor of the tendon sheath occurring in the hands and feet of young and middle-aged adults
  • Calcifying aponeurotic fibroma: It is a rare, painless, and slow-growing tumor mass. Children and young individuals are affected the most by this tumor type
  • Sclerotic fibroma: It is a rare, benign skin tumor that may be present on the face and extremities. It is generally seen in adults
  • Nuchal-type fibroma: It is a rare and benign accumulation of collagen that presents as a tumor on the nape of the neck (nuchal region), just below the skin. The condition may occur at any age
  • Gardner fibroma: It is a benign, irregular tumor of collagen mass that is often seen with Gardner-type familial adenomatous polyposis (FAP). The fibroma is usually present near the spinal cord and is mostly detected in young children
  • Pleomorphic fibroma: It is a benign tumor of the skin tissue that usually develops in adults
  • Elastofibroma: It is an uncommon benign tumor of unknown cause that is found in elderly adults. The most prominent location of the tumor is the back
  • Collagenous fibroma
• Superficial acral fibromyxoma: It is an uncommon, benign tumor of the soft tissues, mostly present around or below the fingernail or toenail. It is observed in a wide age range of individuals
• Cutaneous myxoma
• Dermatomyofibroma: It is a rare, benign tumor of skin that generally affects young women. It is a painless and commonly occurs on the chest or back
• Myofibroma and myofibromatosis: Myofibroma is a rare and benign, perivascular tumor affecting the limbs or head and neck region. It is considered as a pediatric tumor since it normally occurs by birth or within 2 years of birth of the child
• Plaque-like CD34+ dermal fibroma
• Nodular fasciitis: It is a benign and rapidly-growing mass that frequently affects the upper extremities (arm, forearm, and hand). The condition affects older children and young adults

Smooth muscle tumors

• Cutaneous leiomyomas and variants
• Cutaneous leiomyosarcoma (atypical smooth muscle tumor): Primary Cutaneous Leiomyosarcoma is a highly-infrequent malignant tumor affecting the skin. The tumor is generally noted in middle-aged and older adults

(Myo)pericytic tumors

• Glomus tumor and variants: It forms a group of uncommon tumors caused by the proliferation of glomus cells, found in the glomus body. These tumors are frequently observed in young adults
• Myopericytoma and variants: It is a rare, benign tumor forming from cells which surround the blood vessels. This tumor frequently involves the lower limbs, and is frequently noted during middle-age
• Angioleiomyoma: It is a benign tumor occurring just below the skin, affecting the smooth muscles of blood vessels. It is generally present in middle-aged adults

Vascular tumors

• Cutaneous angiosarcoma: It is an infrequent, aggressive, and often rapidly developing tumor, without signs and symptoms in the early stages. It may affect a wide range of age groups
• Hemangioendotheliomas: These describe several types of vascular neoplasms and includes both benign and malignant growths. These tumors may be diagnosed in both children and adults
  • Composite hemangioendothelioma: It is an extremely rare, aggressive tumor, involving blood vessel components. This tumor is considered to be a low-grade malignant proliferation. They are known to manifest during early-to-late adulthood
  • Kaposiform hemangioendothelioma: It is an infrequent and aggressive childhood tumor, involving the blood vessels. These tumors may be located on the skin surface, or deep inside the body tissues
  • Pseudomyogenic hemangioendothelioma: It is a very uncommon tumor of the soft tissues that are potentially malignant. These tumors are known to rarely metastasize. It may develop in individuals of any age group
  • Retiform hemangioendothelioma: It is an infrequent, potentially aggressive tumor, involving the blood vessels that branch out like a tree. It is mostly observed in young and middle-aged adults
  • Epithelioid hemangioendothelioma: It is a tumor involving the blood vessels and surrounding epithelioid cells. The tumor may occur in individuals of any age group
• Kaposi sarcoma: It is a malignant tumor that is associated with human herpes virus infection (HHV8 infection). It may affect individuals of any age group
• Atypical vascular lesion
• Cutaneous epithelioid angiomatous nodule
• Hemangiomas
  • Cherry hemangioma: It is a benign growth composed of small blood vessels that occur on skin tissues. These growths are typically small, cherry-red papules that are often observed in adults over 30 years of age
  • Sinusoidal hemangioma: It is a benign lesion composed of small blood vessels that occur on the skin or deep inside the skin tissues, mostly in the trunk and upper limbs. These hemangiomas are usually observed in women
  • Microvenular hemangioma: It is an uncommon type of hemangioma that may develop in children or adults. It occurs as an asymptomatic solitary skin lesion with a bright red appearance in most cases
  • Hobnail hemangioma: It is an uncommon type of hemangioma, which are benign growths composed of small blood vessels occurring on the skin or within the skin tissues. These tumors are mostly observed in young and middle-aged adults
  • Glomeruloid hemangioma: It is a rare, benign growth composed of small blood vessels that occur on skin tissues, anywhere in the body. These tumors occur frequently in individuals with POEMS syndrome
  • Spindle cell hemangioma: It is a special type of hemangioma (benign growths composed of small blood vessels) that occur on the skin or within skin tissues, anywhere in the body. It is most common in young adults
  • Epithelioid hemangioma: It is a rare, benign tumor involving the blood vessels and surrounding epithelioid cells. Individuals between the age 20-50 years are most commonly affected
  • Tufted hemangioma
  • Angiokeratoma: It is a benign condition consisting of small-sized papules that mostly occur on the scrotum and vulva. It is mostly seen in young adult men and women
  • Infantile hemangioma
  • Congenital non-progressive hemangiomas: rapidly involuting congenital hemangioma and non-involuting congenital hemangioma
  • Lobular capillary hemangioma
  • Verrucous venous malformation
  • Arteriovenous malformation
• Lymphangioma (superficial lymphatic malformation): It is a benign tumor type that develops spontaneously, due to certain abnormalities in the lymphatic system. The tumor can occur either before birth, or shortly after birth

Neural tumors

• Neurofibroma and variants: Neurofibroma is a type of peripheral nerve sheath tumor (PNST). This tumor may arise from the nerves underneath the skin surface, or from nerves deep within the body. It is noted during teenage and young adulthood
• Solitary circumscribed neuroma
• Dermal nerve sheath myxoma
• Perineurioma: It is a rare tumor of the perineurial cells, a type of cells that are present around a peripheral nerve sheath. It can affect both children and adults
• Granular cell tumor: It is a common benign tumor of the soft tissue, which can occur anywhere in the body. the tumor usually seen between the ages of 30 and 50 years
• Schwannoma: These are a group of tumors that arise from the Schwann cells around the nerves; these tumors are essentially nerve sheath tumors. They are commonly seen in young, middle-aged, and slightly older adults
• Malignant peripheral nerve sheath tumor: It is a type of soft tissue sarcoma that typically occur in older adults, when there is no history of neurofibromatosis type 1

Tumors of uncertain differentiation

• Atypical fibroxanthoma and variants: It is a benign, skin-based tumor mostly observed in elderly adults. The tumor develops on sun-exposed skin surfaces and is generally caused by ultraviolet radiation
• Pleomorphic dermal sarcoma
• Myxofibrosarcoma: These form a group of malignant soft tissue tumors that are commonly observed in older adults. A majority of the tumors involve the arms and legs
• Epithelioid sarcoma: It is a type of soft tissue tumor involving the epithelioid cells and connective tissues. It has a high malignancy potential. This tumor is usually observed in teenage and young adults
• Dermal clear cell sarcoma
• Ewing sarcoma: Primary Cutaneous Ewing’s Sarcoma (PCES) is a very rare, life-threatening and malignant skin tumor that affects older children
• Primitive non-neural granular cell tumor
• Cellular neurothekeoma: It is a benign tumor affecting the covering of the nerves, called the nerve sheath. The condition commonly occurs in young individuals

Inherited tumor syndromes associated with skin malignancies:

• Familial melanoma
• Xeroderma pigmentosum: It is a rare inherited genetic condition characterized by extreme sensitivity to ultraviolet rays from the sunlight. The symptoms typically occur during infancy or early childhood
• Nevoid basal cell carcinoma syndrome (Gorlin syndrome)
• Carney complex: It comprises a combination of medical conditions that includes multiple tumors, such as myxomas, schwannomas, endocrine disorders, and pigmented skin conditions. It is a highly infrequent genetic disorder
• BAP1 tumor predisposition syndrome
• Muir-Torre syndrome: It is a rare, genetic disorder with presentation of symptoms occurring at a mean age of 55 years. In this disorder, there is at least one sebaceous gland neoplasm on skin

Additional skin tumor articles (on DoveMed) that are not part of WHO Classification of Skin Tumors:

Acantholytic Acanthoma: It is a rare, benign tumor of skin that is mostly found on the chest, back, arms, and legs. These may occur in a wide age range of adults.

Achromic Nevus: It is a common birthmark that is observed in males and females. Some are diagnosed at birth or noticed within the first few years of a child’s life.

Acral Lentiginous Melanoma: It is an uncommon type of melanoma of skin that typically affects older adults. The condition mostly affects the palms of the hands and soles of the feet.

Adenoid Cystic Carcinoma (ACC) of Lip: It is a very rare and unusual form of cancer. This form of malignancy is typically observed in middle-aged and older adults.

AIDS-Associated Lymphoma of Skin: It can either be a B-cell or a T-cell lymphoma. B-cell lymphomas are far more common than T-cell lymphomas. The condition occurs against a background of AIDS or HIV infection.

Anaplastic Large Cell Lymphoma-involving Skin: It is a T-cell non-Hodgkin’s lymphoma. This type of lymphoma involves other parts of the body first, such as peripheral blood, lymph nodes, bone marrow, and other organs, and skin involvement occurs later. The condition generally affects adults.

Angiofibroma of Skin: It is a common benign tumor of the skin that is usually present on the nose or cheeks. These tumors are usually seen during middle-age.

Angiomyolipoma of Skin: It is a very uncommon extrarenal angiomyolipoma that may be present as a subcutaneous swollen lesion in the body. The tumor is seen among a wide age range of individuals, including children and adults.

Apocrine Hidrocystoma of Skin: It is a rare condition in which there is a dilated cyst of the apocrine sweat glands. It is an uncommon tumor that occurs on the skin as a painless nodule. The condition is common in young adulthood.

Apocrine Spiradenoma: It is a slow-growing and usually solitary tumor that occurs as a painful nodule. It is often seen in young to older adults and can be present anywhere in the body.

Arteriovenous Hemangioma: It is a rare, benign vascular abnormality involving a complex grid of interconnecting arterial and venous structures. It is an acquired condition and is usually seen in children and young adults.

Atypical Melanocytic Nevus of the Genital Type: It is a histological subtype of genital nevus. A majority of them are observed in adult women.

Atypical Mole Syndrome: It is a disorder marked by a large number of atypical moles on skin. It is   usually present in adults rather than children. The condition is often hereditary in nature.

Becker’s Nevus: It is considered to be a pigmented hamartoma of skin; a hamartoma is a developmental anomaly. The condition is observed during early childhood or adolescence.

Benign Capillary Hemangioma: It is one of the most common type of hemangioma that can be either present from birth or develop later in life.

Benign Glomus Tumors: These tumors are usually present superficially and characterized by pain, swelling, and skin discoloration. Some benign tumors may also be located deeper inside the body tissues. These tumors are frequently observed in young adults.

Blue Rubber Bleb Nevus Syndrome: It is a very rare condition in which there are a number of vascular malformations on the skin and other internal organs of the body. The condition is generally manifested at birth.

Bowenoid Papulosis: It is described as a ‘mostly’ benign condition affecting the skin of the genitalia. Its presence is manifested in the form of multiple small fleshy lesions. The condition is noted in sexually-active adults; typically, in young males.

Chondroid Syringoma: It is a slow-growing and usually solitary tumor that occurs as a painless nodule. It is often seen in middle-aged and older adults and is frequently present in the head and neck region.

Common Mole: It is benign tumor of melanocytic cells that occur on the skin. It is typically an acquired condition but may be present at birth or form at any age.

Compound Common Mole: It is a type of common mole. In this type, the melanocytes are present both in the dermo-epidermal junction and in the dermis. It may be present at birth or form at any age in an individual.

Congenital Generalized Fibromatosis: It is a rare condition affecting infants or young children. It is characterized by a spontaneous formation of single or multiple tumors (mostly benign) all over the body.

Congenital Melanocytic Nevus, Superficial Type: It is a common melanocytic mole that is present at birth on the skin of the baby. It may be present anywhere on the body.

Cutaneous Superficial Angiomyxoma: It is an uncommon and benign, mucin-producing tumor of myxoid cells affecting the skin. It is generally seen in middle-aged and older adults.

Cystic Sebaceous Tumor: It is a benign tumor of the sebaceous gland occurring on the skin, which is almost exclusively associated with Muir-Torre syndrome. The condition is mostly seen in young adults.

Dedifferentiated Liposarcomas: These are slow-growing, malignant soft tissue tumors. These tumors are typically present in the retroperitoneum (abdominal cavity) followed by the limbs. The condition is observed with a higher incidence in men.

Desmoplastic Melanoma of Skin: It is an uncommon subtype of cutaneous melanoma that usually arises from sun-exposed skin sites. It is seen in young and old adults.

Diffuse Cutaneous Neurofibroma: It is a common form of neurofibroma that occurs on skin. The condition generally begins to appear in teenage and young adulthood phase of life.

Digital Papillary Carcinoma of Skin: It is an uncommon and aggressively malignant tumor that frequently infiltrates local tissues and bones. It is also known to recur and metastasize. This malignancy is typically observed in middle-aged and older adults.

Eccrine Hidrocystoma of Skin: It is a rare condition in which there is a dilated cyst of the eccrine sweat glands. It is an uncommon tumor that occurs on the skin as a painless papule or nodule. It can occur in young adults.

Eccrine Spiradenoma: It is a slow-growing and usually solitary tumor that occurs as a painful nodule. It is often seen in young to older adults and can be present anywhere in the body.

Elephantiasis Neuromatosa: It is an advanced form of plexiform neurofibroma, in which the entire extremity (arm or leg) is involved. It may be seen in individuals of a wide age group.

Epidermal Inclusion Cyst: It is a very common and benign skin cyst that is usually seen in young and middle-aged adults.

Epidermal Nevus: It is a benign, yellowish-brown, wart-like skin lesion, which is commonly present at birth or develops during childhood.

Epidermolytic Acanthoma: It is a benign tumor of skin that can form on any part of the body. It is an uncommon skin condition that occurs in a wide range of individuals including young children and older adults.

Epithelial Inclusion Cysts of Skin: These are types of skin cysts that form due to entrapment of the surrounding epithelial tissue. These benign cysts are observed in both adults and children.

Familial Cutaneous Collagenoma: It is a connective tissue nevus characterized by multiple, flesh-colored asymptomatic nodules distributed symmetrically on the trunk and upper arms, manifesting around adolescence.

Focal Acral Hyperkeratosis: It is a rare, benign skin condition, wherein there is a formation of tiny papules or plaques on the hands and feet. It is a genetic disorder that may be inherited in an autosomal dominant manner. may be observed in a wide age range of individuals.

Generalized Eruptive Keratoacanthomas: It describes a very uncommon and itchy disorder that is characterized by the presence of numerous firm bumps on several parts of the body such as the arms and legs, chest and back, and face. It is generally observed in middle-aged adults.

Giant Congenital Melanocytic Nevus: It may be described as a very large birthmark with a diameter greater than 20 cm. Congenital melanocytic nevus (CMN) is a common melanocytic mole that is present at birth or develops immediately following the birth of the child.

Granulomatous Mycosis Fungoides: It is a rare variant of mycosis fungoides, which is a cutaneous T-cell non-Hodgkin’s lymphoma. It is generally noted in adults.

Hair-Follicle Nevus: It is a very rare, benign nodule of the hair follicles on skin. These nodules are described as hamartomas (tumor-like benign malformations). It can occur in children, adolescents, and young adults.

Hemosiderotic Fibrolipomatous Tumor: It is an infrequent tumor of the soft tissues, occurring mostly in the subcutaneous tissues of the lower extremity (leg), with a potential for aggressive behavior. The condition occurs in slightly older adults.

Hereditary Neurocutaneous Angioma: It is an extremely uncommon and recently described congenital genetic disorder that is manifested by the presence of skin and brain lesions (called angiomas).

Hydroa Vacciniforme-like Cutaneous T-Cell Lymphoma: It is a rare T-cell non-Hodgkin’s lymphoma that is observed in children. The skin lesions are observed on sun-exposed areas of the body, usually in adults.

Inclusion Body Fibromatosis: It is a rare, benign tumor of specific types of cells in the body, called fibroblasts and myofibroblasts. The condition is usually observed in young children, in the first year of their birth.

Inflammatory Linear Verrucous Epidermal Nevus: It is an extremely rare skin condition that results in the formation of itchy skin lesions, due to epidermis overgrowth. It typically occurs in the first 6 months of life (in very young children).

Ink Spot Lentigo: It is an uncommon dark pigmented skin lesion with irregular borders mostly observed on sun-exposed areas of fair-skinned individuals.

Intradermal Common Mole: It is a type of common mole. In this type, the melanocytes are located exclusively in the dermis. Both children and adults may present this type of nevus.

Inverted Follicular Keratosis: It is a benign tumor of the hair follicles, generally observed in middle-aged and older men.

Junctional Common Mole: It is a type of common mole. In this type, the melanocytes are confined to the dermo-epidermal junction of the skin. Both children and adults may present this type of nevus

Juvenile Hyaline Fibromatosis: It is a highly infrequent genetic disorder affecting infant children, resulting in the formation of multiple subcutaneous nodules.

Keratotic Basal Cell Carcinoma of Skin: It is an uncommon type of basal cell carcinoma that appear as numerous small papules on the skin. The condition generally affects older adults.

Lentigo Maligna: It is a type of melanoma in situ of skin that is generally seen as a solitary pigmented lesion on the head and neck region. It generally occurs in older adults following severe sun-exposure and skin damage.

Linear Unilateral Basal Cell Nevus: It is an uncommon benign tumor of hair follicle. It is mostly observed at or following the birth of the child.

Lipofibromatosis: It is a highly infrequent benign tumor of fatty tissues typically seen in children. Some of these tumors are known to have a congenital presentation.

Lipomatosis: It is a benign condition of fatty tissue overgrowth when abnormal levels of fat are spread over a wide area in the body. Generally, very young children are observed with Lipomatosis.

Localized Cutaneous Neurofibroma: It is the most common clinical form of neurofibroma that occurs on the skin. It is often sporadic in nature and is not present in association with neurofibromatosis type 1 (NF-1) genetic disorder. The condition generally begins to appear in teenage and young adulthood phase of life.

Lymphangioma Circumscriptum: It can be described as small clusters of blisters filled with lymph fluid. It is the most common type of lymphangioma affecting the skin. It usually forms before the birth of the child, or within a few years after birth.

Maculopapular Cutaneous Mastocytosis: It is the most common form of mastocytosis. Most cases are observed during the first 12 months following the birth of the child.

Malignant Granular Cell Tumor: It is very rare variant of granular cell tumor that shows a tendency of becoming malignant. It is usually seen between the ages of 30 and 50 years.

Malignant Pilomatricoma: It is an extremely rare tumor that may develop spontaneously, when there is no history of benign pilomatricoma. In many cases, the malignancy may also occur from benign pilomatricomas. The condition usually occurs in older adults.

Mastocytoma of Skin: It is a form of cutaneous mastocytosis typically appearing as a single skin lesion that is red/yellow brown in color. The condition is predominantly observed during the first 12 months following the birth of the child.

Melanoacanthoma: It is a rare benign tumor of the sebaceous gland on skin. It is commonly seen in middle-aged and elderly adults.

Melanoma In Situ of Skin: Melanomas that are confined to the epidermis and have not yet penetrated through the basement membrane are called so. These may occur in young as well as old individuals.

Melanoma of Nail Unit: It is a melanoma that affects the nail - either the fingernail or the toenail. It may affect the nail bed or nail sides and is capable of spreading to other parts of the body. It is more commonly observed in middle-aged and older adults.

Metastatic Cancer of Skin: It is a condition where cancers originating from various parts of the body spread to the skin. The condition is usually noted in older adults.

Metastatic Squamous Cell Carcinoma of Skin: It is the advanced form of squamous cell carcinoma of skin; a common malignant skin tumor that typically affects elderly men and women.

Minimal Deviation Melanoma (MDM) of Skin: It comprises a group of lesions described as nevomelanocytic tumors. These tumors are generally uncommon and mostly observed in young adults and older children.

Mucinous Nevus: It is a benign skin mole that may be present as a group of papules and plaques on the back, chest, or buttocks. The nevus is often noted before early adulthood.

Multicentric Reticulohistiocytosis: It is a systemic and severe disorder that primarily involves the skin, mucus membranes, and joints. The age of onset is typically in adulthood.

Myxoid Liposarcomas: These are slow-growing, malignant soft tissue tumors. These tumors are typically present on the limbs and observed in both men and women.

Nerve Sheath Myxoma: It is a benign tumor affecting the covering of the nerves, called the nerve sheath. The tumor commonly occurs in middle-aged adults.

Neurofibroma of Skin: It is a common, benign tumor that appears as a small bump on the skin. It is a nerve tumor that arises from the nerves underneath the skin surface (subcutaneously). These tumors are generally observed in young adults.

Neurotized Nevus: It is a type of mole in which, the melanocytes are in the dermis. Over time, there is fibrosis around the melanocytes resulting in a benign Neurotized Nevus. The condition may be present at birth or form at any age.

Nevus Anemicus: It is a skin disorder of congenital origin that presents hypopigmented macules. The condition may be present at birth but noticed during early childhood.

Nevus Comedonicus: It is a rare skin abnormality that affects the folliculosebaceous glands. It is characterized by closely situated, elevated papules on skin, causing blackheads. It can occur at birth, or anytime up to middle age.

Nevus Lipomatosus: It is a rare, benign tumor of the soft tissue, which may develop anywhere in the body. They may occur as nodules or plaques on the skin and can affect individuals of any age group.

Nevus Sebaceous: It is a congenital malformation that occurs as a plaque. It may be present at birth or develop at any age in an individual.

Oral Malignant Melanoma: It is a very rare type of mucosal melanoma that develops from the mucus membrane lining the oral cavity. Middle-aged and older men and women are generally affected by this form of malignancy.

Pacinian Neuroma of the Foot: It is an uncommon tumor that is caused by multiple, repeated trauma. In this condition, painful lesions form on the foot. It is mostly observed in middle-aged adults.

Pacinian Neuroma of the Hand: It is an uncommon tumor that is caused by multiple, repeated trauma. In this condition, painful lesions form on the hand. It is mostly observed in middle-aged adults.

Pacinian Neuroma: It is an uncommon tumor that is caused by multiple, repeated trauma. In this condition, painful lesions form on the hand, foot, or even the vulva. It is mostly observed in middle-aged adults.

Palisaded Encapsulated Neuroma: It is a painless benign tumor of the nerve fibers. The tumor arises with no history of prior injury or trauma. It is often seen in middle-aged and older adults.

Palmar Fibromatosis: It is a common condition that affects the soft tissues of the hands and fingers. It typically causes painless nodules in the volar aspect of the hand. Palmar Fibromatosis is mostly seen in men.

Persistent Melanocytic Nevus: It is recurrence of benign melanocytic nevi at the site of its surgical removal. This takes place due to an incomplete removal of the skin lesion.

Pilar Leiomyoma: It is a rare, benign tumor that originates from the arrector pili smooth muscle. It is usually observed in teens and young adults.

Plantar Fibromatosis: It is a very rare condition that affects one’s feet. It causes nodules in the plantar aspect of the foot. The condition is generally seen in younger individuals.

Plexiform Neurofibroma: It is an uncommon form of neurofibroma that is slow-growing and asymptomatic. A majority of these tumors are benign. The condition is noted in teens and young adults.

Plexiform Schwannoma: It is a histological subtype of schwannoma that affects children. Plexiform Schwannoma affects multiple nerves in the body.

Primary Cutaneous Blastic Natural Killer Cell Lymphoma: It is a very rare condition, and few cases have been reported in middle-aged and older adults. It is an aggressive skin malignancy that may manifest as single or multiple cutaneous lesions.

Primary Cutaneous Diffuse Large B-Cell Lymphoma: It is a cutaneous B-cell non-Hodgkin’s lymphoma. It is a type of diffuse large B-cell lymphoma that affects middle-aged and older adults.

Primary Cutaneous Extramammary Paget’s Disease: It may be associated with an internal unrelated malignancy in as many as one-third of the cases. The condition is typically observed in older adults.

Primary Cutaneous Follicular Center Lymphoma: It is a cutaneous B-cell non-Hodgkin’s lymphoma. It is a common type of lymphoma of skin that affects middle-aged and older adults.

Primary Cutaneous Peripheral T-Cell Lymphoma, NOS: It is a rare cutaneous T-cell non-Hodgkin’s lymphoma that is difficult to be diagnosed. The condition is more common in adults.

Primary Cutaneous, Small-Medium, CD4-Positive, T-Cell Lymphoma: It is a primary cutaneous T-cell non-Hodgkin’s lymphoma. It is a rare kind of T-cell lymphoma that is generally seen as a single patch on the head and neck region or trunk. It generally affects adults.

Progressive Lymphangioma of Skin: It is an acquired condition that manifests as a benign vascular tumor of the skin and subcutaneous tissues in adults.

Proliferating Tricholemmal Tumor: It is a solitary tumor that is usually present on the scalp of elderly adults. It can present both benign and malignant behavior.

Psammomatous Melanotic Schwannoma: It is a rare tumor of the soft tissue, occurring usually beneath the skin (subcutaneously). It is mostly seen to occur in individuals with Carney complex.

Pseudovascular Squamous Cell Carcinoma (SCC) of Skin: It is a very rare malignant tumor of skin that typically affects elderly men and women.

Rhabdomyomatous Mesenchymal Hamartoma (RMH) of Skin: It is an extremely rare, benign tumor of the skeletal muscle fibers and skin. It is observed in infants and young children.

Sebaceous Cyst of Skin: It is a benign superficial cyst that forms on skin when the sebaceous glands (oil glands) that lubricate the skin and hair get obstructed due to various reasons. The condition is observed in adults and children.

Sebaceous Hyperplasia: It is a common, benign overgrowth of the sebaceous gland on skin, which appears as a yellowish tan papule. It is commonly observed in middle-aged and older adults.

Sebaceous Trichofolliculoma: It is a type of folliculoma with sebaceous differentiation. It is very similar to a trichofolliculoma, which is a rare and benign tumor of the hair follicles. The condition is more common during puberty, adolescence, and early adulthood.

Secondary Cutaneous Extramammary Paget Disease: It is the term used when Paget’s disease develops secondary to systemic disease; meaning that the condition affects internal organs first, before affecting skin. It is typically observed in older adults.

Skin Involvement in Hodgkin Lymphoma: It is very rare condition that takes place secondary to systemic disease, meaning that the disease affects other body organs first, before affecting skin. Hodgkin lymphomas may be observed in both children and adults.

Skin Tag: It is a very common, benign tumor that appears as a pedunculated polyp on skin. Skin tags are commonly found in adults.

Small Cell Melanoma of Skin: It is a rare and uncommon variant of nevoid malignant melanoma of skin. These lesions are diagnostically challenging and may be initially misdiagnosed. It is mostly seen in adults over 30 years old.

Smooth Muscle Hamartoma (SMH) of Skin: It is a benign overgrowth of smooth muscle cells on the body. A hamartoma is a developmental anomaly. The condition is commonly present at birth (congenital manifestation).

Solar Lentigo: It is a common benign condition characterized by dark skin spots on the face and back of the hands, which develops in middle-aged and older adults typically following exposure to long-term sunlight (ultraviolet radiation).

Spindle Cell Lipoma: It is a benign, subcutaneous tumor of fat that is predominantly observed in middle-aged and older men.

Spiradenocarcinoma of Skin: It is a very rare, malignant tumor of the sweat glands. It is a longstanding tumor that normally occurs on the upper and lower limbs in adults.

Spitzoid Melanoma of Skin: It is a rare tumor that is described as a variant of nevoid melanoma of skin. These tumors are generally observed more in adults than children.

Subungual Glomus Tumor: It is a type of glomus tumor of the nail affecting the tissue beneath the nail. It may affect individuals of any age group.

Subungual Melanoma: It is melanoma of the nail affecting the tissue beneath the nail base, also known as the nail matrix. It is more commonly observed in middle-aged and older adults.

Syringocystadenoma Papilliferum: It is a slow-growing and usually solitary tumor that occurs as a painful nodule. It is often seen in children and young adults, generally in the head and neck region.

Syringotropic Mycosis Fungoides: It is a rare variant of mycosis fungoides, which is a cutaneous T-cell non-Hodgkin’s lymphoma. It is usually present as a single, well-defined plaque. It is generally noted in adults.

Traumatic Neuroma: It is the benign proliferation of a nerve, due to a prior injury or trauma. It may occur at any age.

Trichilemmal Cyst: It is the second most common cyst of skin that is usually observed in adults. It occurs on the skin as a painless nodule.

Trichodiscoma: It is a rare, slow-growing, and usually benign tumor of the hair follicles. It is generally observed in young and middle-aged adults.

Tubular Apocrine Adenoma of Skin: It is a benign tumor that arises from the apocrine sweat gland. It is a relatively uncommon tumor that may occur at any age (seen in both children and adults).

Tubular Carcinoma of Skin: It is an uncommon malignant tumor that some researchers believe arise from the apocrine sweat glands. It is more common in the 30-60 years’ age group.

Tufted Angioma: It is an uncommon vascular tumor that is mostly seen in young children and young adults. It can grow very slowly and affect large skin areas on the body.

Ungual Melanoma: It is melanoma of the nail affecting the sensitive tissue immediately below the nail, also known as the nail bed. It is more commonly observed in middle-aged and older adults.

Well-Differentiated Liposarcomas: These are usually slow-growing, malignant soft tissue tumors. They are well-circumscribed and typically present on the retroperitoneum, limbs, and mediastinum (chest region). The condition is observed with a higher incidence in men.