NMIBC happens when cancer cells grow in the tissue that lines the inside of the bladder but do not reach any layers of bladder muscle. The bladder is the organ that holds urine. Its muscles contract to push urine out through the urethra when you urinate. The muscles are under the bladder lining and layers of tissue, so cancer that starts in the lining can eventually grow down into the muscle, somewhat like tree roots. The LAUREL study is for people with Ta or T1 tumors that has not yet grown into the bladder muscle.