Since the late 1980s, veterinarians have been baffled by a particularly aggressive and relatively uncommon form of cancer found in cats. Now researchers at the North Carolina State University College of Veterinary Medicine are working to determine what is causing the cancer, and how it can be prevented.
Vaccine-associated feline sarcoma is a cancer of the connective tissues beneath the skin that occurs at the site of an immunization. It happens in a small number of cats, but is very aggressive and difficult to control.
Since the late 1980s, veterinarians have noticed inflammatory reactions in cats between three and five weeks after a vaccination, according to Dr. Mac Law, assistant professor of pathology at NC State. The vaccine reaction starts as a small lump at the site of the injection. Some of the reactive cats later developed an aggressive connective tissue tumor, called sarcoma.
Reactions have occurred after common vaccinations such as those for rabies and the feline leukemia virus. While most feline cancer happens in older cats, researchers have discovered that this type of cancer may occur in cats of any age.
"Suddenly, veterinarians are caught in this situation -- we want to recommend that clients vaccinate their cats, and then the public starts to hear that some cats are getting these really nasty tumors," Law said.
Law and his colleagues are asking area veterinarians to refer to them cats that have developed vaccine reactions for the study. Cats will receive a free physical examination, complete blood count, chemistry panel, urinalysis, biopsy and histopathology at the College of Veterinary Medicine
According to Law, there has been research into the tumors themselves, but very few researchers have investigated the possible linkage between the inflammation that occurs at an injection site and cancer.
"The big question we're trying to answer is what's the connection," Law said. "We didn't have this problem 20 to 30 years ago, so I suspect part of the answer may lie in the vaccines or components within them," he said.
He believes it's possible that the adjuvant in the vaccine may play a role. The adjuvant helps boost the body's immune response to fight off the disease the vaccine is intended to prevent, but it also causes inflammation at the site of the injection. This inflammation causes free radicals -- harmful byproducts of cell metabolism -- to circulate in the area. The free radicals damage the DNA in the inflamed tissue, possibly causing mutations to occur in the DNA. In rare cases, this can lead to cancer. However, Law notes that some researchers have discovered feline sarcomas in cats that received vaccines without adjuvants.
Since mutations to DNA are the source of all cancers, Law's research will focus on what changes are happening to the cat's DNA and why. Researchers believe that for some reason, cats are not well equipped to handle the inflammation. Dogs, in contrast, don't appear to be nearly as susceptible to this form of cancer.
Law hopes his research will lead to a test to help determine what components of vaccines may be causing cancer. He also hopes to learn more about granulomatis myositis, a human reaction to vaccines in which persistent muscle inflammation occurs. Vaccination-associated fibrosarcoma has not been reported in humans.
Law has researched veterinary cancer for 10 years. He has teamed up with two veterinary oncologists at NC State, Drs. Marlene Hauck and Laurel Williams, for this project.
Their research is funded by the Vaccine-Associated Feline Sarcoma Task Force, which is jointly sponsored by the American Veterinary Medical Association, the American Animal Hospital Association, the American Association of Feline Practitioners, the Veterinary Cancer Society and several vaccine manufacturers. - By Greg Thomas
[Contact: Dr. Mac Law, Greg Thomas ]