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Cat Vaccine-Site Sarcomas

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Cat Vaccine-Site Sarcomas


Vaccine-site sarcomas can be called many different things. They are known as injection-site sarcomas, vaccine-associated fibrosarcomas et al. These are tumors that are believed to be caused by vaccinations. They are very rare but can happen if your cat has immune system reactions to the vaccine.

Sarcomas are malignant tumors that are composed of connective tissue cells. They are quick to develop and are subject to metastasis.

They were initially identified in the 1980's when vaccines began to be developed differently than in the past. The live vaccines were discontinued and the new vaccines were developed with dead viruses. Aluminum was added to the vaccines and there are some that believe that this is cause.

These sarcomas do not always appear immediately after your cat is vaccinated. They can appear as long as 9 years after the first inoculation. While they appear to be localized, there are branches that can spread into the healthy tissue that surround the site. When surgery is performed to remove the tumor the fingers/branches can stay and contribute to metastasis. It is estimated that over half of the sarcomas that are removed will recur within half a year.

There are several different types of vaccine-site sarcomas. They can be fibrosarcoma, osteosarcoma, Cat Myxosarcoma, Cat Liposarcoma and other types as well. The name is indicative of the area in which the tumor originates.

Signs and Symptoms

As you run your hand over your cat, you need to be aware of any abnormal lump under the skin in the various areas that your cat has previously had their vaccinations. The usual places are behind the neck and the back of the legs.


If you notice a mass, nodule or some swelling under the skin, take it seriously. Schedule an appointment with your veterinarian to have it examined. This is especially true if the lump remains present for several months. If the swelling is noticed soon after the vaccination, get your cat to your vet as soon as possible.

Your vet will perform a physical examination to feel the lump and evaluate it. This will be followed by fine needle aspirate. This can tell your vet the type of tumor that has developed. Although this process is good for staging, it is not particularly conclusive for identifying the type of tumor. Some tumors do not shed cells that can be obtained with a needle aspiration. After the needle aspiration your veterinarian will perform a biopsy. This will remove a small portion of the mass to examine under a microscope.

X-rays of the surrounding areas will be done in an effort to determine whether metastasis has occurred.

Treatment Options

These are very aggressive tumors and there will most likely be more than one course of treatment necessary. Your vet will perform surgery to remove the obvious mass and this will be followed by Cat Radiation Therapy and Cat Cancer Chemotherapy.

Home Care

Observe your cat. Be especially aware of the area that the mass was removed. You will be making routine visits to your veterinarian so that he or she can keep a close check on your dog’s rehabilitation.


The only prevention is the elimination of vaccinations. This is may not be an option as it is illegal in some states to not vaccinate your cat. It is therefore important to continue your scheduled vaccinations. There are some vaccines that are given every three years instead of every year. This may be your preference.

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