Veterinary immunizations routinely given to cats for feline leukemia and rabies may increase the risk of malignant tumors developing where the vaccines are typically administered, according to UC Davis researchers. They believe, however, that the benefits of immunizing animals against disease still far exceed the risks involved. "Each year approximately 20 cases of fibrosarcomas (malignant tumors) are diagnosed per 100,000 cats seen by veterinarians in California, while the incidence of post-vaccination tumors is estimated to be about one case for every 10,000 doses of feline leukemia virus or rabies virus vaccine," says veterinary epidemiologist Dr. Philip H. Kass, who reported the findings with colleagues this month in the Journal of the American Veterinary Medical Association. To lower the risk, the researchers recommend that vaccination sites be varied and that records of various vaccination locations and vaccine types become part of the animals' permanent health history. Additionally, they recommend that all benefits and risks of vaccination be discussed with cat owners until such time that vaccines for cats are shown to be free of possible harmful health effects.