Injection Site Sarcomas In Cats

Feline Injection Site Sarcomas (FISS) are extremely aggressive cancers that may be related to an injection or vaccination. The specific cause is unknown. They can develop from 3 months to 4 years post vaccination, or injection, and some don’t show up for five or more years. Recurrence rates after surgery vary form 51% to 86% depending upon how aggressive the surgery is and if radiation therapy is instituted. Higher grade cancers can also spread or metastasize to the lungs. Depending on the study, these cancers can seen as often as 1 in 1000 cats or 1 in 10,000. 

What I See and Hear

Fortunately, I don’t see these cancers very often. However, when I do see them, they are usually related to end of life situations even when the kitty’s parents have gone to extreme lengths to deal with them. Major surgery may have been unsuccessful with recurrence of the cancer, or the caretakers elected not to have surgery done due to the poor prognosis when the tumor was finally diagnosed. Whatever course was chosen, the end result can be devastating to both the patient and the kitty’s parents because of the aggressive nature of this cancer. I would recommend that if you find even a tiny bump in/on your cat’s skin, no matter the location, have it checked as soon as possible. Early detection can improve the long term survival rate significantly. 

Important Information

This cancer was first determined to be related to rabies vaccinations 20 years ago. In 1987, Pennsylvania enacted the first mandatory feline rabies law for cats residing in that state. Pathologists at the University of Pennsylvania then found a 61% increase in this form of cancer beginning shortly after the rabies program was started. Research indicated that the way certain inactivated feline vaccines were manufactured with an adjuvant (an additive to increase the body’s immune response) seemed to cause chronic inflammation at the injection site and it was hypothesized, but never proven, this was likely the instigating factor for this form of sarcoma. Other possible causes considered, are long acting corticosteroids (depo-medrol) and penicillins, damage to the skin and nylon sutures left in too long. All cause chronic inflammation in the skin that may then transform into cancer in a small percentage of cats. Genetic predisposition also seems to be an important factor. For more information and assessment of risks related to vaccinations, read the following articles. Discuss with your veterinarian the risks involved with any long acting injectable medication as well as the possibility of using vaccines that do not contain and adjuvant. For more detailed information, click on the buttons below.