Mollyspal,
Well that sucks! You're certainly not the first to wind up with a different cancer. I would think though that it is better than if it were bladder cancer that had spread. Still sucks though. Sorry to hear it and hope they are able to take care of it with just the colectomy and that they got it soon enough to get rid of it.
It would seem (although I have done no research and haven't looked for any studies) that bladder cancer folks should probably be sure to get regular colon checks as well.
My reasoning is that if bladder cancer is likley caused by carcinogens being stored for excretion from the body, then both types of excretions would be vulnerable. Again, no studies that I've looked at but it just seems logical. Not that medicine is necessarily logical but sometimes things just seem to make sense. Of course, I could be all wrong and often am--just ask my wife...she'll tell ya!
Best of luck! One thing at a time...
Mike