4470 El Camino Real

Los Altos, California 94022

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Vaccine Induced Sarcoma in Cats

Fluffy, a ten year old, neutered, domestic, longhaired male cat, was brought to Adobe Animal Hospital to have a lump on his back checked that the owners had just noticed. Fluffy was feeling good and acting normally and the lump didn't seem to bother him. He was current on his vaccinations having received his last set a year previously.

Fluffy's physical exam was normal except for the lump, which was located just behind his shoulder blades. We performed a fine needle aspirate, where an needle and syringe is used to withdraw some cells from the lump. Under microscopic exam, we could see a group of cells that were somewhat spindle-shaped. As groups of cells such as these can be a marker for cancer, we recommended getting a biopsy to the lab and the owners agreed.

Fluffy was not willing to let us do the biopsy with local anesthetic, so we used an intravenous injection to put him under. The biopsy was simple and quick, done with a large needle-like instrument called a TruCut biopsy needle. We sent the sample to the lab for analysis.

Unfortunately, the biopsy results came back as a fibrosarcoma, possibly vaccine induced. Normally fibrosarcomas are not too common and when found early and completely removed, the animal can be cured. Fibrosarcomas caused by vaccines are much more aggressive and require serious surgery. Usually, the way to tell vaccine-induced fibrosarcoma from regular fibrosarcoma, is by the location of the tumor and by how aggressive its growth. The area behind the shoulder blades is a common place to give vaccines since the skin is so loose. Since this was the location of Fluffy's tumor, we were very concerned that this was a vaccine-induced sarcoma.

We recommended aggressive surgery along with radiation therapy in order to give Fluffy the best chance for a long remission. Vaccine-induced sarcomas carry a guarded prognosis due to the aggressive nature of these tumors. Fluffy's owners wanted to do all they could to optimize his chances. They were referred to an oncologist so the radiation therapy could be done at the time the surgeon was removing the tumor.

Fluffy's surgery went well, although he was pretty sore for a few weeks. Aggressive treatment required partial removal of one of his shoulder blades, naturally necessitating a longer convalescence. Radiation therapy totaled twelve treatments, each Monday Wednesday, and Friday for five weeks. Fluffy handled the necessary anesthesia with flying colors, or actually, changing colors since the only side effect was that his hair grew back white instead of brown tabby. It was a new look for him, but a good one.

It has been one year since Fluffy's diagnosis and he is still going strong. His owners are hopeful for another year with him. The treatment for these tumors is a new strategy and so far, most cats are surviving from one to two years after treatment before microscopic tumor cells spread to the lungs or return to the original surgery site where they are even harder to remove.

About 1 in 10,000 cats will develop a tumor from vaccinations, so a genetic component is suspected. Fluffy no longer gets vaccinated due to his obvious genetic tendency to get these tumors. Until we know what causes this problem, we do not recommend vaccinating indoor cats for either rabies or feline leukemia virus, two vaccines which are most implicated in causing the tumors, since the risk of cancer would be higher than the risk of disease.

Species: Cat

Diagnosis: Vaccine induced sarcoma

Doctor: Cristi Derenzi

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