Bladder cancer happens in the tissues of the bladder, the organ that holds urine. There are three types of bladder cancer: transitional cell carcinoma, the most common bladder cancer type, which begins in the transitional cells in the inner layer of the bladder; squamous cell carcinoma, a rare cancer triggered when squamous cells form in the bladder after a long-term infection or irritation; and adenocarcinoma, another rare cancer that starts when glandular cells form in the bladder after long-lasting bladder inflammation and irritation.