Urinary tract (ureter, urinary bladder, and urethra) tumors 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.

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 Urinary and Male Genital Tumors (2019), 5th Ed., Vol. 8, benign and malignant tumors of the urinary tract are classified in the following manner:

Tumors of the urinary tract:

• Tumors of the urinary tract

Urothelial tumors

• Non-invasive urothelial neoplasms
  • Urothelial papilloma: It is an uncommon and benign subtype of noninvasive lesion of the urothelium. It is a solitary lesion that is commonly found around the urinary bladder
  • Inverted urothelial papilloma: It is a rare benign tumor of the urinary bladder that is mostly seen in elderly adults, particularly in men
  • Papillary urothelial neoplasm of low malignant potential: It is a subtype of noninvasive urothelial neoplasm. It may be described as a premalignant lesion involving the genitourinary (GU) tract. The tumor predominantly occurs in the urinary bladder
  • Non-invasive papillary urothelial carcinoma, low-grade: It is form of noninvasive urothelial neoplasm that is diagnosed under the microscope, on examination of the cancer cells by a pathologist. It is reported that a diagnosis of the tumor is very challenging
  • Non-invasive papillary urothelial carcinoma, high-grade: It is a very rare form of noninvasive urothelial neoplasm that is diagnosed under the microscope, on examination of the cancer cells by a pathologist
  • Urothelial carcinoma in situ: It is a flat urothelial lesion that forms very commonly in the urinary bladder urothelium. It is described as a high-grade non-invasive malignant condition, where the abnormal cancer cells have not spread beyond the site of initial growth
• Invasive urothelial neoplasms
  • Invasive urothelial carcinoma

Squamous cell neoplasms of the urinary tract

• Urothelial squamous cell papilloma: It is an extremely rare and benign subtype of squamous cell neoplasm. Most of these lesions are seen in the urinary bladder, and sometimes in the urethra
• Squamous cell carcinomas of the urinary tract
  • Verrucous carcinoma of the bladder: It is an extremely rare form of bladder cancer. Verrucous carcinoma is described as an uncommon and well-differentiated subtype of squamous cell carcinoma
  • Pure urothelial squamous cell carcinoma: It is a rare histological variant of urinary tract cancer that mostly arises in the urinary bladder. It is mainly observed in certain parts of the world, where a parasitic infection, known as schistosomiasis, is commonly seen

Glandular neoplasms

• Adenomas
  • Villous adenoma: It is an exceedingly rare tumor arising in the urinary bladder, from the urothelium. Most of the cases are observed in middle-aged and older adults, and a male predominance is noted
• Adenocarcinomas
  • Adenocarcinoma NOS: It is a rare malignant tumor of the urothelial epithelium with glandular differentiation, typically affecting middle-aged and older men

Urachal and diverticular neoplasms

• Urachal carcinoma: It is a rare malignancy of the urinary tract that arises from the urachus. Urachal Carcinomas are generally observed in middle-aged and older adults
• Diverticular carcinoma: It is a rare malignant tumor that arises from the diverticulum of the urinary tract. The diverticulum is an outpouching that occurs abnormally

Urethral neoplasms

• Urethral accessory gland carcinomas
  • Littre gland carcinoma of the urethra: It is a very rare malignant tumor that arises from the urethral glands of Littre located in the male urethra
  • Skene gland carcinoma of the urethra: It is an exceedingly rare malignant tumor that arises in the female urethra
  • Cowper gland adenocarcinoma of the urethra: It is a malignant tumor that arises in the Cowper gland around the urethra in men

Tumors of Mullerian type

• Clear cell adenocarcinoma of the urinary tract: It is an extremely rare form of malignancy that is often noted in the urethra. Individuals of any age group may present the tumor, and a strong female predilection is seen
• Endometrioid carcinoma of the urinary tract: It is an exceedingly rare form of malignancy that is noted in the urinary bladder. It is believed that the tumor origin is associated with ectopic Müllerian embryogenesis

Additional urinary tract tumor articles (on DoveMed) that are not part of WHO Classification of Urinary and Male Genital Tumors:

Angiomyolipoma of Urinary Bladder: It is an extremely uncommon extrarenal angiomyolipoma that may be present in adult men and women. An angiomyolipoma is a benign tumor that is a mixture of blood vessels, smooth muscles, and fat.

Arteriovenous Malformation of Urinary Bladder: It is an extremely uncommon formation that may arise in children and adults. An arteriovenous malformation is an abnormal connection between the veins and arteries resulting in collection of vascular malformation.

Bladder Cancer: It is a general term for cancer that originates in the urinary bladder (hence Urinary Bladder Cancer). There are different types of Bladder Cancers. A majority of these types are diagnosed at an early stage, more commonly in men.

Clear Cell (Glycogen-Rich) Urothelial Carcinoma: It is an extremely rare and aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Diffuse Large B-Cell Lymphoma (DLBCL) of Urinary Bladder: It is a B-cell non-Hodgkin’s lymphoma that affects middle-aged and older adults. It is a subtype of lymphoma of the urinary bladder.

Giant Cell Urothelial Carcinoma: It is a highly-infrequent and aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Infiltrating Urothelial Carcinoma: It is a very common subtype of invasive urothelial carcinoma (UCC), which is the most common form of bladder cancer. The carcinoma is generally observed in middle-aged and older adults.

Inflammatory Myofibroblastic Tumor of Urinary Bladder: It is a very rare, mostly benign tumor of the urinary bladder. Even though it is an uncommon tumor within the genitourinary system, the urinary bladder is a common site.

Large Cell Neuroendocrine Carcinoma (LCNEC) of the Urinary Bladder: It is a rare high-grade neuroendocrine tumor that is seen in the urinary tract.

Lipid-Rich Urothelial Carcinoma: It is an extremely rare and aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Lymphoepithelioma-like Urothelial Carcinoma (LELC): It is a rare subtype of invasive urothelial carcinoma, a form of malignancy of the urothelium.

Lymphoma of Urinary Bladder (LUB): It is an uncommon lymphoma that is mostly observed in middle-aged women. The condition may be primary or secondary.

MALT Lymphoma of Urinary Bladder: It is a rare non-gastric type of extranodal marginal zone lymphoma. It affects the urinary bladder in older adults.

Microcystic Urothelial Carcinoma (MUC): It is a rare and highly-aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Micropapillary Urothelial Carcinoma: It is a rare aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Mixed Neuroendocrine Neoplasm of the Urinary Bladder: It is a rare high-grade neuroendocrine tumor that is seen in the urinary tract.

Nested Urothelial Carcinoma: It is a rare and aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Paraganglioma (PGL) of the Urinary Bladder: It is an uncommon neuroendocrine neoplasm that involves the urinary bladder wall.

Plasmacytoid Urothelial Carcinoma (PUC): It is a recently classified, rare, and aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Poorly-Differentiated Urothelial Carcinoma: It is an extremely rare and aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Postoperative Spindle-Cell Nodule of Urinary Bladder: It is a rare and benign tumor that forms due to an injury (tissue damage), typically arising from a surgical procedure involving the genitourinary tract.

Sarcomatoid Urothelial Carcinoma (SUC): It is an extremely rare and highly-aggressive subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium.

Small Cell Neuroendocrine Carcinoma (SCNEC) of the Urinary Bladder: It is a rare high-grade neuroendocrine tumor that is seen in the urinary tract.

Solitary Fibrous Tumor (SFT) of Urinary Bladder: It is a mostly benign overgrowth arising from the mesenchymal tissue. The tumor is observed in young and old adults.

Transitional Cell Cancer of the Renal Pelvis and Ureter: It is a term used to describe the transformation of normal cells to cancer cells in the renal pelvis (part of the kidney) and ureter. The ureters carry urine from the kidneys to the urinary bladder.

Ureteral Fibroepithelial Polyp: It is an uncommon benign tumor that affects the ureters (a pair of tubes that carry urine from the kidneys to the urinary bladder). The tumor is seen among a wide range of adults and children.

Ureteritis Cystica: It is a rare benign condition that appears as a tumor/mass within the ureters; the ureters are tubes that help transport urine from the kidneys to the urinary bladder.

Urothelial Carcinoma (UCC): It is the most common form of bladder cancer; UCC constitutes over 90% of the cases and are high-grade malignancies.

Urothelial Carcinoma with Divergent Differentiation: It is a subtype of invasive urothelial carcinoma (UCC), a form of malignancy of the urothelium. The divergent differentiation observed may be squamous, glandular, or trophoblastic differentiation type.

Urothelial Dysplasia: It is the abnormal growth of cells on the urothelium. It can progress to carcinoma in situ in future, and hence, it is important to diagnose and treat the condition early.

Urothelial Proliferation of Uncertain Malignant Potential (UPUMP): It is a recently described and rare subtype of noninvasive lesion of the urothelium. This premalignant lesion can be seen sporadically or concurrently with preexistent bladder neoplasms.