The Risk of Feline Injection-site Sarcoma

According to the American Association of Feline Practitioners, the risk of a cat developing sarcoma following vaccination is less than 1 in 10,000 doses. However, when sarcoma does develop it is associated with high recurrence and mortality rates. In fact, due to the potential for development of aggressive cancer, the AAFP recommends that vaccinations be administered in the lower legs rather than in the interscapular region to facilitate complete tumor removal by limb amputation in the event that feline injection-site sarcoma (FISS) occurs.

An article in the December 2018 issue of the Journal of the American Veterinary Medical Association (JAVMA) recaps several studies and reports detailing the likelihood of FISS development and the level of concern veterinarians should have about its prevalence.

Feline Inject-Site Sarcoma Research

The veterinary community was first made aware of FISS following a 1991 letter to the editor that appeared in JAVMA and alluded to a potential association between rabies vaccinations in cats and the development of FISS. Fast-forward 27 years and “there are currently no known management options to prevent or cure FISS,” said Apryl Steele, DVM, 2019 AAFP president. In the years since the initial letter was written, numerous studies have been conducted to examine the incidence, pathophysiology, diagnosis, prognosis, and treatment of FISS.

Initial research suggested that the risk of FISS development was about 2 cases per 10,000 doses of vaccine. Over time that estimate increased to 13 to 36 cases per 10,000 doses, but more recent epidemiologic studies suggest that the risk is actually much lower, thus establishing the current belief that FISS occurs in fewer than 1 cat per 10,000 doses of vaccine administered.

Following publication of the AAFP’s 2013 Feline Vaccination Advisory Panel Report, a University of Florida pilot study found that administering vaccines in the distal part of the tail was well tolerated and elicited similar serologic responses to vaccination in the distal limbs. A 2017 study from Cornell University found that a feature of FISS is DNA damage, noting that response mechanisms to DNA damage can promote multidrug resistance, rendering adjunctive radiotherapy or chemotherapy mostly ineffective as treatment. Instead, aggressive surgery—often resulting in limb amputation—is the recommended course of treatment.

Current Vaccine Recommendations

As quoted in JAVMA, Karen Stasiak, MSN, DVM, veterinary medical lead for pet care biologicals at Zoetis, said 1 recommendation for FISS prevention is to inject cats only as necessary, whether with a vaccine, medication, or microchip. This recommendation is in accordance with current AAFP guidelines, which state: “The veterinarian should undertake a clinical risk/benefit assessment for each animal and discuss recommended vaccination schedules with the owner so that they can make an informed choice. The assessment should include discussion on the likelihood of exposure, the health and lifestyle of the animal, and the risks related to vaccination.”

While studies are ongoing to pinpoint a definitive cause of FISS and to find more effective, less invasive forms of treatment, much of the veterinary community remains in agreement that the risk of sarcoma development does not outweigh the need to vaccinate cats against key infectious diseases.