There are several types of bladder cancer, with urothelial carcinoma being the most common at about 90% of cases. This cancer begins in the urothelial cells lining the bladder. Less common types include adenocarcinoma in 1% of cases related to colon cancer, small cell carcinoma in another 1% starting in nerve-like cells and spreading rapidly, and squamous cell carcinoma making up about 5% of cases starting in flat cells and more common where schistosomiasis infections exist. The rarest type is sarcoma beginning in bladder muscle cells and having several subtypes.