There is a study I found a couple years ago run by the veterinary equivalent of the AMA. I can't remember the exact link but you can do a search using Yahoo or whatever. One thing I remember is that some vaccines have additives called "adjuvants" which may be the actual agents triggering cancer in some cats. You may wish to ask your vet about "adjuvent-free" shots.

Another good strategy is vaccinating every three years (in my area you can get a three year distemper and three year rabies.) Also, stagger the shots (don't give them all at one go.)