Bladder cancer is categorized by a number of types, depending on where exactly it forms, along with other factors. The most common type of bladder cancer is transitional cell (urothelial) carcinoma (TCC). This type accounts for about 95 percent of bladder cancers. Cancer cells of this type look like the urothelial cells lining the inside of the bladder. There are two subtypes of TCC:
Papillary carcinoma: Grows out from the inner surface of the bladder toward the hollow center in finger-like projections. Often, these tumors are called noninvasive papillary cancers, meaning they don’t grow into the deeper layers of the bladder wall. When papillary TCC is very low grade, it may be called papillary neoplasm of low-malignant potential, and treatments typically have positive outcomes.
Flat carcinomas: This type of TCC does not grow out of the urothelium toward the center of the bladder. Rather, flat carcinomas remain on the surface of the bladder wall. If a flat carcinoma is confined to the urothelium, it is called noninvasive flat carcinoma or flat carcinoma in situ.
Rarer forms of bladder cancer include:
Squamous cell carcinoma accounts for about 1 percent to 2 percent of bladder cancers diagnosed in the United States. Squamous cells look similar to the flat cells on the surface of the skin. Almost all squamous cell carcinomas of the bladder are invasive.
Adenocarcinoma of the bladder closely resembles the gland-forming cells seen in colon cancers, and accounts for about 1 percent of bladder cancers in the United States.
Small-cell carcinoma is extremely rare, accounting for fewer than 1 percent of all bladder cancers diagnosed in the United States. This type of bladder cancer begins in neuroendocrine cells, which are similar to nerves.
Sarcoma is another very rare type of bladder cancer that begins in the muscle layer of the bladder wall.