PD's often look pretty hard at research experience, and most consider it a definite plus. But they're not necessarilly insisting that it's Derm research.
I guess there's a reason you're thinking about bladder epithelial cells. If you have what you consider a good opportunity and is interested, go for it. You don't HAVE to do derm research, but rather show that you have an interest and aptitude for research. Nobody expects you to get the next Lasker or Nobel Prize, or find the foolproof marker for Melanoma in order to get a residency.
So if you think you can get something published, go for it. A publication in even something not remotely associated with derm is better than a derm-project which never gets off the ground.
