Testing the Addition of an Anti-Cancer Drug, Gemcitabine, to Usual Treatment (BCG Alone) in People Whose Non-Muscle Invasive Bladder Cancer (NMIBC) Came Back After Prior BCG Therapy

This phase III trial compares the effect of adding gemcitabine to intravesical Bacillus Calmette Guerin (BCG) versus intravesical BCG alone in patients with non-muscle invasive bladder cancer that has come back after a period of improvement (recurrent). Gemcitabine is a chemotherapy drug that blocks the cells from making deoxyribonucleic acid (DNA) and may kill cancer cells. Intravesical BCG is a solution containing the live BCG bacteria that is placed in the bladder via a catheter (intravesical). When the solution comes into direct contact with the bladder wall, it stimulates the body's immune system which kills tumor cells. Giving gemcitabine with intravesical BCG may kill more tumor cells in patients with recurrent non-muscle invasive bladder cancer.