Bladder cancer is a type of cancer that affects the bladder, which is an organ in the urinary system responsible for storing and expelling urine. It occurs when normal cells in the bladder change and grow uncontrollably, forming a tumor. There are several types of bladder cancer, including transitional cell carcinoma (the most common type), squamous cell carcinoma, adenocarcinoma, and small cell carcinoma. The cause of bladder cancer is not fully understood, but risk factors include smoking, exposure to certain chemicals or radiation, a family history of the disease, and having a urinary catheter in place for an extended period. Treatment options depend on the stage of the cancer and may include surgery, chemotherapy, radiation therapy, immunotherapy, or targeted therapy.