What is it?

Tumors of the breast 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 tumors diagnosed via lab studies (biopsy) are benign. Malignant breast tumors are invasive breast carcinomas of ductal or lobular type.

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 Tumors of the Breast (2019), 5th Ed., Vol. 2, benign and malignant breast tumors are classified in the following manner:

Epithelial tumors of the breast:

• Benign epithelial proliferations and precursors
  • Usual ductal hyperplasia: It is a benign proliferation of breast duct cells. It is a fairly common condition generally seen in middle-aged and older women
  • Columnar cell lesions, including flat epithelial atypia: It is a recently introduced terminology in the WHO classification. A diagnosis of the condition is made when breast lesions do not have the classical features of atypical ductal hyperplasia or low-grade ductal carcinoma in situ of breast
  • Atypical ductal hyperplasia: It is an atypical condition of breast which is often diagnosed under the microscope by a pathologist. The condition is often detected during routine mammogram screening and is seen in both men and women
• Adenosis and benign sclerosing lesions
  • Sclerosing adenosis: It is a benign tumor of breast affecting the lobes in the breast tissue. There may be extensive involvement of the tissues by this benign tumor. This tumor type is observed in young women
  • Apocrine adenosis and adenoma: It is a benign tumor of breast affecting the breast tissue. These are observed in young and old women
  • Microglandular adenosis: It is a rare and benign tumor of breast affecting the lobes in the breast tissue. There may be extensive involvement of the tissues by this benign tumor
  • Radial scar / complex sclerosing lesion: These are benign breast tumors that mimic malignant tumors. These lesions are mostly observed in young and middle-aged women
• Adenomas
  • Tubular adenoma: It is a benign tumor of breast commonly affecting young women. The tumor resembles breast fibroadenomas in its characteristic features
  • Lactating adenoma: It is a type of tubular adenoma that occurs in mothers who are breastfeeding or in women during pregnancy
  • Ductal adenoma: It is a benign tumor of breast affecting the glandular tissue of breast and the milk ducts. This tumor type is mostly observed in middle-aged and older women
• Epithelial-myoepithelial tumors
  • Pleomorphic adenoma: It is a rare benign tumor of the breast that is observed in a wide age range of individuals. The tumor bears close resemblance to pleomorphic adenoma of the salivary glands
  • Adenomyoepithelioma: It is a rare benign tumor of the breast affecting the lobes in the breast tissue and observed in women of all ages. The tumor is associated with cancer, since it can undergo malignant transformation
  • Malignant adenomyoepithelioma: It is a rare form of breast cancer. When there is a malignant transformation occurring within an adenomyoepithelioma, it is called malignant adenomyoepithelioma
• Papillary neoplasms
  • Intraductal papilloma: It is a benign tumor that can be present anywhere from near the nipple region to the lobular units (the terminating units of the milk duct) inside the breast
  • Papillary ductal carcinoma in situ: It is a type of non-invasive malignant breast tumor that is diagnosed under the microscope by a pathologist on examination of the tumor cells
  • Encapsulated papillary carcinoma: It is a rare subtype of breast cancer. It is diagnosed under the microscope by a pathologist on examination of the tumor cells. The condition is generally noted in post-menopausal (older) women
  • Solid papillary carcinoma (in situ and invasive): These are special types of malignant breast tumors that are diagnosed under the microscope by a pathologist on examination of the tumor cells. Many of the tumors show neuroendocrine differentiation
  • Invasive papillary carcinoma: It is a specific type of invasive ductal carcinoma (or infiltrating ductal carcinoma) of breast that initially affects the milk ducts and moves on to involve other parts of the breast. A majority of this cancer type is observed in post-menopausal women
• Non-invasive lobular neoplasia
  • Atypical lobular hyperplasia: It is an atypical condition of the breast that is usually diagnosed under the microscope by a pathologist. It may be described as an atypical non-invasive neoplasm of the terminal duct lobules of breast
  • Lobular carcinoma in situ: It is a non-invasive malignant breast tumor that originates in the terminal duct lobular units of the breast. It is suspected that LCIS of Breast is a precursor lesion for invasive breast cancer
• Ductal carcinoma in situ
  • Ductal carcinoma in situ: It is a non-invasive malignant breast tumor. In this condition, the malignant tumor cells are confined to the breast ducts. It is often suggested that DCIS of Breast is a precursor lesion for invasive breast cancer
• Invasive breast carcinoma
  • Invasive breast carcinoma of no special type: These are invasive breast cancers that have a tendency to be aggressive and spread to other local and regional sites. This subset comprises the largest group and also form the most common type of breast cancers
  • Microinvasive carcinoma: It is a rare tumor of the breast that usually occur in a background of in situ carcinomas (such as high-grade ductal carcinoma in situ), and the invasive component by definition is less than 1 mm
  • Invasive lobular carcinoma: It is a type of invasive breast cancer having a tendency to be aggressive and spread. This subset comprises about 10-15% of invasive breast cancers and affect women over the age of 50 years
  • Tubular carcinoma: It is a rare and special type of breast cancer that is mostly observed in older women. This breast cancer is relatively easier to diagnose during a screening mammogram
  • Cribriform carcinoma: It is a rare type of invasive breast cancer, with a prognosis that is much better than invasive ductal carcinomas of breast. This type is mostly observed in middle-aged and slightly older women
  • Mucinous carcinoma: It is a rare type of breast carcinoma that produces mucin (a type of mucus-like protein). It is observed as a soft mass in the breast, in women around the age of 60 years
  • Mucinous cystadenocarcinoma: It is an extremely rare type of mucinous breast cancer that is observed in middle-aged and older women. This subtype is differentiated based on the histopathological examination of a breast biopsy specimen by a pathologist
  • Invasive micropapillary carcinoma: It is a specific type of invasive ductal carcinoma of breast that initially affects the milk ducts and moves on to involve other parts of the breast
  • Carcinoma with apocrine differentiation: It is a rare subtype of invasive breast carcinoma that presents apocrine differentiation when the tumor cells are observed under the microscope by a pathologist
  • Metaplastic carcinoma: These carcinomas form a diverse group of rare breast tumors with features of adenocarcinoma, spindle cell, and squamous cell carcinomas. These tumors are mostly observed in middle-aged and elderly women
• Rare and salivary gland-type tumors
  • Acinic cell carcinoma: It is a rare type of breast carcinoma that is mostly observed in women after the age of 35 years. This subtype is differentiated based on the histopathological examination of a specimen by the pathologist
  • Adenoid cystic carcinoma: It is a rare type of breast carcinoma that is mostly observed in women after the age of 50 years. This low-grade tumor is considered to be mildly aggressive
  • Secretory carcinoma: It is a rare low-grade tumor of the breast affecting females. It appears like a honey-combed structure characterized by milk-like secretions on the cells, during a histopathological examination of a specimen by the pathologist
  • Mucoepidermoid carcinoma: It is an extremely rare type of invasive breast carcinoma. This histological subtype is diagnosed when the tumor cells are observed under the microscope by a pathologist
  • Polymorphous adenocarcinoma: It is an extremely rare type of invasive breast carcinoma. This histological subtype is diagnosed when the tumor cells are observed under the microscope by a pathologist
  • Tall cell carcinoma with reversed polarity: It is a rare histological subtype of invasive breast carcinoma. It is diagnosed under the microscope by a pathologist on examination of the tumor cells
• Neuroendocrine neoplasms
  • Neuroendocrine tumor: It forms a group of neuroendocrine tumors that show similar morphological features to other NETs such as of the lung and GI tract. It consists of both benign and malignant tumors. These tumors are mostly observed in women after the age of 50 years
  • Neuroendocrine carcinoma: It is a rare subtype of invasive breast carcinoma that presents neuroendocrine differentiation when the tumor cells are observed under the microscope by a pathologist. This form of malignancy is generally observed in middle-aged and older adults

Fibroepithelial tumors and hamartomas of the breast:

• Fibroepithelial tumors and hamartomas of the breast
  • Hamartoma: It is a rare benign tumor of breast tissue, mainly affecting middle-aged women during the time of menopause (perimenopausal period)
• Fibro-epithelial tumors 
  • Fibroadenoma: It is a benign tumor that forms in the breast. Typically, the size of a marble, these tumors are characterized by its firm and smooth shape, as well as their rubbery feel
  • Phyllodes tumor: It is a rare tumor of the breast that is observed in middle-aged individuals (mostly women). The most common site of phyllodes tumor is the breast

Tumors of the nipple:

• Tumors of the nipple
• Epithelial tumors
  • Syringomatous tumor: It is an uncommon and benign tumor that originates from the sweat glands, seen on the nipple or areolar region in females (girls and women)
  • Nipple adenoma: It may be described as an abnormal collection of a special type of cells that forms a mass around the nipple ducts. It is a benign condition mostly seen in adult women
  • Paget disease of the breast: It is a rare form of breast cancer that starts from the nipple and extends to the areola around the nipple. The malignancy is most commonly seen in women over the age of 50 years

Mesenchymal tumors of the breast:

• Mesenchymal tumors of the breast
• Vascular tumors
  • Hemangioma: It is a benign malformation occurring in the breast. It is observed in a wide age range (both children and adults are affected)
  • Angiomatosis: It is a very rare and benign vascular tumor of breast affecting young, middle-aged, and slightly older women. It is known to grow to large sizes
  • Atypical vascular lesions: These are small (numerous) lesions seen on the skin of the breast post radiation treatment. These lesions are strictly confined to the area of irradiation and may arise after a few years of radiation therapy
  • Postradiation angiosarcoma of the breast: It is a highly-aggressive tumor that occurs secondary to irradiation to the breast region and surrounding skin; the malignancy develops as a complication of the radiation therapy
  • Primary angiosarcoma of the breast: It is an infrequent, aggressive, and often rapidly developing tumor that presents no signs and symptoms in the early stages. The tumor arises from the vascular linings that involve the blood vessels
• Fibroblastic and myofibroblastic tumors
  • Nodular fasciitis: It is a rare and rapidly growing benign mass involving the breast skin and breast tissues, presenting tenderness and pain (in some individuals)
  • Myofibroblastoma: It may be described as an unusual, benign, soft tissue tumor of the breast that is mostly observed in middle-aged and older men and women
  • Desmoid fibromatosis: It is a benign tumor of the connective tissues of the body. Even though benign, the tumor displays local aggression and can invade uncontrollably into the surrounding tissues and structures. In many cases, the tumor involves the abdomen region; breast is an uncommon site for this tumor
  • Inflammatory myofibroblastic tumor: It is a very rare and mostly benign tumor affecting the breast. The tumor generally affects younger populations, especially females
• Peripheral nerve sheath tumors
  • Schwannoma: It is a very rare and mostly benign breast tumor that arise from the Schwann cells around the nerves; these tumors are essentially nerve sheath tumors that are mostly seen in older adults
  • Neurofibroma: It is a common benign tumor that mostly appears as a superficial tumor on the breast in both men and women. Neurofibromas are nerve tumors that arise from the nerves underneath the skin surface
  • Granular cell tumor: It is a common benign tumor of the soft tissue that can occur anywhere in the body. When it occurs in the breast tissue, it is known as GCT of Breast. This tumor is uncommon and occurs more frequently in women than men
• Smooth muscle tumors
  • Leiomyoma: It is a benign tumor of breast affecting the nipple and areola. It is observed in young, middle-aged, and older individuals. A leiomyoma is a benign smooth muscle tumor that can develop anywhere in the body, but the breast is an uncommon site
  • Leiomyosarcoma: It is a rare type of malignant connective tissue tumor. The age of presentation is usually between 30 and 70 years. Leiomyosarcoma occurs in the muscles that are not voluntarily controlled, known as smooth muscles
• Adipocytic tumors
  • Lipoma: It is a common benign tumor of fat tissues (adipose tissues). They are usually observed in adults between the ages of 40 and 60 years. Lipomas can occur in almost any part of the body subcutaneously
  • Angiolipoma: It is an uncommon solitary and painless tumor affecting individuals of a wide age group. There are no predisposing factors reported for the tumor, and the cause is presently unknown
  • Liposarcoma: It is a type of carcinoma of breast that affect women of a wide age category. A liposarcoma is a rare and malignant tumor of the fat cells. It is generally asymptomatic and can occur anywhere in the body
• Other mesenchymal tumors and tumor-like conditions
  • Pseudoangiomatous stromal hyperplasia: It is a rare, benign tumor of breast that is observed in young and old women. It is usually discovered incidentally, during a screening mammography. The tumor may also be misdiagnosed as a fibroadenoma

Hematolymphoid tumors of the breast:

• Hematolymphoid tumors of the breast
• Lymphoma: It is an uncommon form of lymphoma that is mostly observed in older women, though a wide age category of women may be affected. The condition may be primary (uncommon) or secondary (commonly noted)
  • Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma): It is a rare non-gastric type of extranodal marginal zone lymphoma. It typically affects the breasts in older women
  • Follicular lymphoma: It is a rare subtype of breast lymphoma that generally affects middle-aged and older women. It can be present as a mass in the breast and cause thickening of the breast with pain
  • Diffuse large B-cell lymphoma: It is a rare B-cell non-Hodgkin’s lymphoma that is typically seen in older women. It is the most common subtype of lymphoma of breast. The condition may be associated with autoimmune disorders
  • Burkitt lymphoma: It is a very aggressive and fast-growing form of non-Hodgkin lymphoma. The lymphoma affects the B-cells of the immune system. It is an uncommon condition that is seen in women who mainly belong to tropical Africa
  • Breast implant-associated anaplastic large cell lymphoma

Tumors of the male breast:

• Tumors of the male breast
• Epithelial tumors
  • Gynecomastia
  • Carcinoma in situ
  • Invasive carcinoma

Metastases to the breast:

• Metastases to the breast

Genetic tumor syndromes of the breast:

• Genetic tumor syndromes of the breast
• Syndromes
  • BRCA1/2-associated hereditary breast and ovarian cancer syndrome: It is a malignant condition inherited in an autosomal dominant manner. Individuals with this condition have germline mutations in the BRCA1 and BRCA2 genes which increases the risk of developing breast and ovarian cancer
  • Cowden syndrome: It is an inherited condition that is characterized primarily by multiple, noncancerous growths (called hamartomas) on various parts of the body
  • Ataxia-telangiectasia: It is an uncommon inherited disorder affecting the brain, spinal cord, and immune system
  • Li-Fraumeni syndrome, TP53-associated: It is caused by mutations in the TP53 gene and is associated with persistent breast cancer. Li-Fraumeni syndrome is a hereditary syndrome that predisposes individual’s to an increased risk for certain cancer types
  • Li-Fraumeni syndrome, CHEK2-associated: It is caused by germline mutations in the CHEK2 gene and is associated with moderately persistent breast cancer. Li-Fraumeni syndrome is a hereditary syndrome that predisposes individual’s to an increased risk for certain cancer types
  • CDH1-associated breast cancer: It is a cancer susceptibility syndrome that is generally characterized by lobular carcinoma (cancer that starts in the cells) of the breast. The syndrome is caused by germline mutations in the CDH1 gene, inherited in an autosomal dominant pattern
  • PALB2-associated cancers: These are caused by germline mutations in the PALB2 gene. The PALB2 gene is a partner gene of the BRCA2 gene, which can increase one’s risk for breast and other cancer types
  • Peutz-Jeghers syndrome: It is a rare autosomal dominant condition that increases one’s susceptibility to developing polyps and certain malignancy types. PJS is a cancer predisposition syndrome
  • Neurofibromatosis type 1: NF1 manifests as benign tumors developing from the layer covering the cutaneous and optic nerves. This results in disfiguring outgrowths from the skin. Neurofibromatosis is a multisystem genetic disorder affecting the nervous system, skin, and skeletal muscles
  • The polygenic component of breast cancer susceptibility

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

Adenocarcinoma of Breast with Spindle Cell Metaplasia: It is initially associated with the milk ducts and can grow into the surrounding breast structures with time. A majority of this cancer type is observed in post-menopausal women.

Adenoid Cystic Carcinoma of the Breast in Men: It is a rare subtype of breast cancer that results in malignant tumor growth. While, ACC of breast is most commonly present in women, it has been known to develop in males as well, although in significantly smaller numbers.

Adenomyoepithelial Adenosis of Breast: It is an extremely rare tumor of breast affecting the lobes in the breast tissue. There may be extensive involvement of the breast tissue by this benign tumor. Even though benign, it can occur in association with other malignancies of the breast.

Adenosis of Breast: It is a common benign tumor of breast affecting the lobes in the breast tissue. There may be extensive involvement of the breast tissue by this benign tumor; it may appear as being locally invasive. It is generally observed in young women.

Adenosquamous Carcinoma of Breast: It is an invasive cancer that belongs to a rare group of tumors known as metaplastic carcinomas of breast. Adenosquamous Breast Carcinomas can be of two types - low-grade and high-grade; a majority of the tumors are low-grade. This breast cancer type is mostly observed in middle-aged and elderly women.

Benign Breast Lumps: It is an overarching term to describe any benign (non-cancerous) tumors or lumps that develop in the breasts. The tumors may form when breast cells begin to grow abnormally at a rapid pace. While they may be painful, they are not known to cause significant signs and symptoms. a few examples include fibroadenomas, granular cell tumors, and intraductal papillomas.

Benign Peripheral Nerve Sheath Tumors of Breast: These are a group of benign tumors affecting the soft tissues or peripheral nerves (nerve sheath) in the breast. These tumors are very rare and are known to occur in young and old individuals (mostly in women).

Benign Phyllodes Tumor of Breast: It is a rare tumor of the breast that is observed in middle-aged individuals (mostly women). In general, phyllodes tumor may be classified as benign, malignant, or borderline based on their behavior. A majority of the tumors behave in a benign manner.

Blunt Duct Adenosis of Breast: It is a rare and benign tumor of breast affecting the lobes in the breast tissue. This type of tumor is typically observed in young women. It may be described as a type of sclerosing adenosis of breast that is diagnosed on a microscopic examination by a pathologist.

Borderline Phyllodes Tumor of Breast: It is a rare tumor of the breast that is observed in middle-aged individuals (mostly women). In general, phyllodes tumor may be classified as benign, malignant, or borderline based on their behavior. Rarely, some tumors show both non-cancerous and cancerous features; these are classified as borderline phyllodes tumors.

Breast Cancer: Breast Cancer is the most common type of cancer diagnosed in women and is believed to be the second-most leading cause of death in women. It is a type of cancer in which certain cells in the breast become abnormal, grow uncontrollably, and form a malignant mass (tumor). Older women have a greater risk than younger women.

Breast Cancer in Men: It is a rare form of cancer that begins in the breast tissue of typically older men. The cancer occurs when normal cells become abnormal and grows uncontrollably, forming a malignant mass (tumor).

Central Papilloma of Breast: It is a benign tumor of breast affecting the central area of the milk duct (near the nipple), which is mostly observed in young and middle-aged women. It is a form of intraductal papilloma.

Columnar Cell Mucinous Carcinoma of Breast: It is an extremely rare type of mucinous breast cancer that is observed in middle-aged and older women. This category is differentiated based on the histopathological examination of a breast biopsy specimen by the pathologist.

Fibromatosis of Breast: It is a rare primary tumor that arises from within the breast tissue. Even though it is benign, the tumor displays local aggression and can invade into the adjoining tissues. Women are affected more during their childbearing phase (middle-aged women present a higher number of cases).

Glycogen-Rich Clear Cell Carcinoma of Breast: It is a rare type of breast carcinoma that is mostly observed in women after the age of 40 years. A majority of the cells of this tumor have glycogen in their cytoplasm, which can be observed during a histopathological examination of a breast biopsy specimen by the pathologist.

Hemangiopericytoma of Breast: It is a rare, low-grade malignant tumor of the mesenchyme; it is described as a type of soft tissue sarcoma. Most cases have been observed in adult women, though some cases have been reported in young children and even men.

Inflammatory Carcinoma of Breast: It is an advanced form of breast carcinoma that may occur secondary to an underlying and invasive breast tumor that causes an obstruction in the breast lymphatic system. The condition is mostly observed in women over 40 years’ old.

Invasive Ductal Carcinoma of Breast (NOS): These are invasive breast cancers, which have a tendency to be aggressive and spread. This subset comprises the largest group and also the most common type of breast cancers. These tumors are mostly observed in women after the age of 40 years.

Invasive Ductal Carcinoma of Breast with Choriocarcinomatous Features: It is an extremely rare subtype of ductal carcinoma of breast, which is almost only observed in women in the 50-70 years’ age group. Invasive ductal carcinomas of breast are invasive breast cancers, which have a tendency to be aggressive and spread.

Invasive Ductal Carcinoma of Breast with Melanotic Features: It is a rare subtype of ductal carcinoma of breast, which affects the breast parenchyma or breast tissue. Invasive ductal carcinomas of breast are invasive breast cancers, which have a tendency to be aggressive and spread.

Invasive Ductal Carcinoma of Breast with Osteoclastic Giant Cells: It is a type of ductal carcinoma of breast that is mostly observed in women after the ages of 40. Invasive ductal carcinomas of breast are invasive breast cancers, which have a tendency to be aggressive and spread.

Lipid-Rich Carcinoma of Breast: It is a type of breast carcinoma that is mostly observed in women over the age of 50. This subtype is differentiated based on the presence of lipids in the cell that is seen on a histopathological examination of the breast biopsy specimen.

Low-Grade Adenosquamous Carcinoma of Breast: It is mostly observed in middle-aged and elderly women. In general, adenosquamous carcinoma of breast is an invasive cancer that belongs to a rare group of tumors known as metaplastic carcinoma of breast.

Malignant Myoepithelioma of Breast: It is an invasive tumor of breast affecting the lobes in the breast tissue. There may be extensive involvement of the tissues by the tumor. This condition is observed in young and old women.

Malignant Phyllodes Tumor of Breast: It is a rare tumor of the breast that is observed in middle-aged individuals (mostly women). In general, phyllodes tumor may be classified as benign, malignant, or borderline based on their behavior. Some tumors are malignant and behave aggressively; they may infiltrate into surrounding tissue structures and metastasize to other body sites.

Mammary Osteosarcoma: It is a type of aggressive breast carcinoma that is mostly observed in Caucasian women (young and old). Osteosarcomas are bone-forming tumors that are highly-cancerous with high-mortality rates.

Medullary Carcinoma of Breast: It is a type of breast carcinoma that is mostly observed in middle-aged and older women. This subtype is identified based on a morphological examination of the breast biopsy specimen by a pathologist.

Mixed Epithelial/Mesenchymal Metaplastic Carcinoma of Breast: It is a type of metaplastic carcinoma of breast that comprises a diverse set of invasive breast cancers combined with features of mesenchymal cells. These uncommon tumor types are mostly observed in women over the age of 35.

Mixed Type Infiltrating Carcinoma of Breast: It is a subtype of invasive carcinoma of breast that is mostly observed in women over the age of 40. This category is differentiated based on the histopathological examination of tumor specimen by a pathologist.

Myoepitheliosis of Breast: It is a benign tumor of breast affecting the milk ducts that is mostly observed in women of all ages that include premenopausal and postmenopausal women.

Oncocytic Carcinoma of Breast: It is a very infrequent type of breast carcinoma that is seen in women over 60 years of age. Oncocytic carcinomas are high-grade tumors that are diagnosed under the microscope by a pathologist.

Peripheral Papilloma of Breast: It is a benign tumor of breast affecting the peripheral breast duct or lobular units that is mostly observed in young and middle-aged women (but can occur in women of all ages).

Pleomorphic Invasive Ductal Carcinoma of Breast: It is a rare type of ductal carcinoma of breast, which is observed in a wide age range of women. This aggressive carcinoma shows the presence of giant cells and adenocarcinoma type features that can be detected on a histopathological examination of the breast biopsy specimen by a pathologist.

Postoperative Spindle-Cell Nodule of Breast: It is a rare and benign tumor that forms due to an injury (tissue damage), typically due to a surgical procedure. It is observed in a wide age range of women. the tumor can appear within a few weeks to a few months following the surgical procedure (such as a needle biopsy).

Primary Atypical Carcinoid Tumor of Breast: It is an extremely rare neuroendocrine tumor of breast that is usually benign but can occasionally behave in a malignant manner. It has similar characteristic features of carcinoid tumor of lung. The tumor is often seen in middle-aged to older women.

Primary Carcinoid Tumor of Breast: It is a neuroendocrine tumor of breast that is usually benign. It has similar characteristic features of carcinoid tumor of lung. Primary tumors of breast are very rare. The breast carcinoid tumor is often seen in middle-aged and older women.

Primary Large Cell Neuroendocrine Carcinoma of Breast: It is a rare type of neuroendocrine breast carcinoma that is mostly observed in middle-aged to older women. Neuroendocrine carcinomas of breast are a group of infiltrating tumors that show similar morphological features to other neuroendocrine tumors such as of lung and GI tract.

Primary Rhabdomyosarcoma of Breast: It is a highly infrequent type of carcinoma of breast, which is observed in a wide age category of individuals (young and old). The primary form of breast tumor is very rare; metastatic sarcoma affecting the breast (secondary tumor) is more commonly noted.

Primary Small Cell Carcinoma of Breast: It is a rare type of primary neuroendocrine breast carcinoma that is mostly observed in middle-aged to older women. Neuroendocrine carcinomas of breast are a group of infiltrating tumors that show similar morphological features to other neuroendocrine tumors such as of lung and GI tract.

Primary Solid Neuroendocrine Carcinoma of Breast: It is a very rare type of neuroendocrine breast carcinoma that is mostly observed in middle-aged to older women. Neuroendocrine carcinomas of breast are a group of infiltrating tumors that show similar morphological features to other neuroendocrine tumors such as of lung and GI tract.

Primary Squamous Cell Carcinoma of Breast: It is a very rare, invasive, primary breast tumor that presents squamous pattern. It belongs to a rare group of tumors known as metaplastic carcinoma of breast. These types are mostly observed in middle-aged and elderly women.

Sebaceous Carcinoma of Breast: It is a primary carcinoma of breast showing sebaceous (related to the skin) differentiation, though skin involvement may not be observed. It is an extremely rare tumor that is observed in middle-aged women.

Signet Ring Cell Carcinoma of Breast: It is a rare mucinous type of carcinoma of breast that is observed as a soft mass in the breast, in women around the age of 40 years. Two types of Signet Ring Cell Carcinomas are observed - one is lobular carcinoma type and the other is similar to diffuse gastric carcinoma.

Solitary Fibrous Tumor of Breast: It is a mostly benign overgrowth arising from mesenchymal tissue. These rare tumors can occur in any part of the body, or in the soft tissues where mesenchymal cells are present. The tumor arises in the breast as a firm mass.