Urothelial carcinoma (also called transitional cell carcinoma) is a cancerous tumour of the bladder that can spread (metastasize) to other parts of the body. Cancerous tumours are also called malignant tumours.
The urothelium (also called the transitional epithelium) is the lining on the inside of the bladder, ureters and urethra, as well as the renal pelvis (the part of the kidney where urine collects). It is made up of urothelial cells, or transitional cells. These cells can become cancerous, which is called urothelial carcinoma (or transitional cell carcinoma). Urothelial carcinoma is the most common type of bladder cancer. It makes up more than 90% of all bladder cancers.
Urothelial carcinoma can start in any part of the urinary tract, including the renal pelvis, ureters, bladder or urethra. People with any type of bladder cancer, including urothelial carcinoma, may also have a similar cancer in another part of the urinary tract. When cancer is found in the bladder, doctors will check the entire urinary tract for other tumours.
Urothelial carcinomas have 2 main growth patterns. Papillary urothelial carcinomas have slim finger-like projections that grow from the lining of the bladder into the bladder cavity. Flat urothelial carcinomas lay flat in the lining of the bladder. They grow deeper into the layers of the bladder wall rather than into the bladder cavity.
Urothelial carcinomas may be non-invasive (only in the lining of the bladder) or invasive (growing into other layers of the bladder wall).
Non-invasive urothelial carcinoma
Non-invasive urothelial carcinomas are only in the lining of the bladder and have not grown deeper into the bladder wall. At the time of diagnosis, 50%–60% of people have non-invasive tumours.
Types of non-invasive urothelial carcinomas include:
- non-invasive flat urothelial carcinoma (also called carcinoma in situ)
- non-invasive papillary urothelial carcinoma, high grade
- non-invasive papillary urothelial carcinoma, low grade
- non-invasive papillary urothelial neoplasm of low malignant potential (which means there is only a small chance that it will become invasive cancer)
Invasive urothelial carcinoma
Invasive urothelial carcinomas grow from the lining of the bladder into the deeper layers of the bladder wall, such as the connective tissue (called the lamina propria) and the muscle layer (called the muscularis). At the time of diagnosis, 40%–50% of people have invasive tumours.
Urothelial carcinomas with mixed epithelial features are invasive tumours that have different types of cells mixed with the cancer cells. They occur less often than typical invasive urothelial carcinomas and are generally considered to be more aggressive. These rare urothelial carcinomas include the following.
Urothelial carcinomas with squamous differentiation have urothelial and squamous cells (a type of epithelial cell that is thin and flat and looks like a fish scale). Squamous cells are in about 21% of urothelial carcinomas in the bladder. They are seen in 44% of renal pelvis tumours.
Urothelial carcinomas with glandular differentiation have gland cells and there are spaces between gland cells when the tumour is looked at under a microscope. Glandular differentiation is seen in 6% of bladder cancers.
Micropapillary urothelial carcinomas have micropapillae (fine finger-like projections) and are high grade.
Sarcomatoid urothelial carcinomas (also called urothelial carcinosarcomas) have cells that look like sarcoma (cancerous connective tissue cells). This aggressive carcinoma has often spread to lymph nodes and organs other than the bladder when it is diagnosed.
Nested variant of urothelial carcinomas have nests, which are groups of anaplastic cells (immature or unspecialized cells) with large nuclei. This carcinoma is very rare but aggressive.
Microcystic urothelial carcinomas are very rare. These tumours have cysts in them that can range in size from microscopic to 2 mm.
Lymphoepithelioma-like urothelial carcinomas have lymphatic tissue (tissues that make up the lymphatic system) mixed with urothelial cells, or transitional cells. This very rare carcinoma is more common in men than women.
Plasmacytoid and lymphoma-like urothelial carcinomas have cells that look like lymphoma (cancerous lymphocytes) or plasmacytoma (cancerous plasma cells).
Giant cell urothelial carcinomas have abnormally large cells with more than one nucleus.
Clear cell urothelial carcinomas have clear cells (cells with clear cytoplasm and a large nucleus).
Lipid cell variant of urothelial carcinomas have cells that are filled with fat.
Undifferentiated variant of urothelial carcinomas have cells that don’t have any clear features and don’t look like any other type of cell (they are undifferentiated).
Urothelial carcinomas with trophoblastic differentiation (mixed with trophoblast cells) have cells that look like trophoblasts. Trophoblast cells form the tissue that becomes the placenta and the membranes that surround the embryo.
Referring to, having to do with or resembling a papilla (nipple-like projection).
For example, a papillary tumour is a tumour shaped like a small nipple or mushroom with the stem attached to the inner lining of an organ.
The group of tissues and organs that produce and store cells that fight infection and diseases.
The lymphatic system includes the adenoids, tonsils, spleen, thymus, lymph nodes, lymph vessels and bone marrow.
Also called the lymph system.