Periodic rabies vaccinations are the law in most states, yet some people are nervous about getting a rabies shot for their pet because they have read reports that cats can get cancer at the injection site. One Catnip reader wrote to say that three months after she went ahead and ordered the rabies injection because she did not want to flout the law, her cat developed some lumps in the area of the hip where the shot was administered. The tumor turned out to be malignant, and his hind leg had to be amputated. The cat did fine getting around on three legs — for 4 months. The lumps returned, the tumor quickly grew huge and ulcerated, and the woman had to have her pet put down. She continues to have a hard time forgiving herself for having her pet vaccinated, and now she’s scared to get her new cat his own vaccinations.
The concern is understandable. It is very hard to try to do right by your cat, only to have your good intentions and follow-through backfire. But can a cat develop cancer at a vaccination site, or is it just a fiction that’s circulating on the Internet?
The truth about vaccinations and cancer
Unfortunately, there is an exceedingly small chance that a cat vaccinated against rabies will develop cancer at the site of the injection. It’s called Feline Injection Site Sarcoma, or FISS, and sometimes occurs in reaction to other vaccinations as well. The American Association of Feline Practitioners puts the risk at “well below” one in 10,000 doses of vaccine.
Some rabies vaccinations are meant to be administered every three years, and others once a year, so it may seem that every three years is the way to go. But while how often a cat receives the vaccine has not been clearly associated with altering the risk for cancer upward or downward, something called a non-adjuvanted one-year “canarypox” rabies vaccine has been developed that appears safe, at least for now.
Note that it’s not all about the content of the vaccine. It appears some cats have a genetic predisposition to experience a negative reaction that influences tissue response at the injection site.
You definitely should not forgo the vaccine, but because of the risk, it is recommended that veterinarians administer rabies vaccinations as low on the leg as possible. Then, in the very rare case that the leg must be amputated after a cancer is excised, the amputation will not be as involved. In some cases, to try to avoid amputation, radiation and/or chemotherapy will be recommended once the FISS is surgically removed. That could help kill any remaining cancer cells that may have been left behind. It’s not a bad idea to get a veterinary oncologist in on that discussion.