Not only bladder cancer but a whole bunch of things. I used to run home from work and I would always pee right beforehand so I wouldn't risk having to find some sort of place to pee, but then I started peeing blood every couple of weeks when my mileage went up to around the 10 mile mark. Apparently hematuria can happen from basically having a totally empty bladder chafe itself raw if you run long enough lol. I quit peeing before leaving work after my doctor recommended giving that a shot and it cleared up