Feline Vaccination Associated Cancer

Vaccine-associated sarcoma

A vaccine-associated sarcoma (VAS) or feline injection-site sarcoma (FISS) is a type of malignant tumor found in cats (and rarely, dogs and ferrets) which has been linked to certain vaccines. VAS has become a concern for veterinarians and cat owners alike and has resulted in changes in recommended vaccine protocols. These sarcomas have been most commonly associated with rabies and feline leukemia virus vaccines, but other vaccines and injected medications have also been implicated

Few people think twice about having their cat vaccinated.

The wide use of pet vaccinations in this country has made diseases such as distemper and rabies rare in U.S. cats.

But vaccinations come with their own set of risks.

For cats, one of the most serious is fibrosarcoma, a type of cancer that appears at the injection site and spreads rapidly.

Fortunately, fibrosarcoma is uncommon, occurring once in approximately 10,000 vaccinations.

But it's often fatal for any cat who develops it.

In the last decade, the veterinary community has come to the realization that the soft tissue tumors they were encountering in some cats may have actually been caused by a vaccine that the cat received.

These soft tissue tumors are difficult to treat, have a high incidence of recurrence, and can lead to death in some cats. As the prevalence of this disease has grown, clients have begun to question the vaccine protocols that have been recommended by their family veterinarian

How fibrosarcoma develops after your cat is vaccinated

A lump may appear at the injection site after your cat receives a vaccination. This is a result of your cat's immune system reacting to the vaccine. The lump should disappear within a few days or a few weeks after the shot.

Sometimes the lump doesn't go away and a tumor appears. At first, small tumors can be successfully removed with surgery, but they tend to recur and become larger each time.

For decades, vaccinations were injected in the loose skin between a cat's shoulder blades. A tumor in this location would eventually become too large to take out because of the amount of skin and tissue that would have to be removed with it. By that time, the cancer had usually spread to the cat's other organs, and the prognosis was grim.

What causes fibrosarcoma?

It's not clear why these tumors form, but studies suggest that it's the adjuvant in the vaccine, not the virus itself. An adjuvant is a substance added to a killed-virus vaccine to enhance the immune system's reaction. In the case of cat vaccines, the adjuvant was aluminum salts, and aluminum has been found in excised tumors.

There are also studies indicating that the frequency of vaccination could contribute to the development of fibrosarcoma.

Accurate diagnosis of feline sarcoma is very important because it determines the treatment procedures that have to be used.

The vet will perform a series of blood tests to determine if the pet has any underlying disease. The signs and symptoms of sarcoma will also help the vet carry out diagnostic tests such as X-rays and scans. Ultrasounds are important to determine the size and density of the tumor. MRI scans are particularly helpful during diagnosis.

After these preliminary tests are performed, the vet will conduct a biopsy of the tumor to find out the grade of the cancer present.

The vet will also find out if the cancer has spread to other parts of the body, especially the lungs. Once the diagnosis is confirmed, the vet will adopt the appropriate treatment protocol to suit the type of sarcoma present.

Treatment of Feline Sarcoma

The most commonly used treatment procedure is surgical removal of the cancerous tumor or cells. If the tumor is located in an area of the body that cannot be easily accessed, the vet will use chemotherapy and radiation therapy to kill cancerous cells and shrink the tumor.

Cats in general respond favorably to chemotherapy.

If the tumor can be completely removed, the cat's chance of survival is much higher. If the cancer is very aggressive in nature and has spread to other parts of the body, the sarcoma may prove fatal. In such cases the vet will only use chemotherapy and supportive care to bring relief to the pet from discomfort.

Another factor that determines prognosis is the chance of recurrence of tumors.

While sarcomas spread in only 10 to 15 percent of sick cats, they can recur in nearly 30 to 70 percent of pets that have already been treated with surgery and chemotherapy. Tumors are generally known to recur within a few months of treatment. While some cats live happy lives for up to two years after successful treatment, a few pets succumb to the disease after several months of initial treatment. As a pet owner, make sure you work with your vet to help relieve the cat's discomfort.

Should I Stop Vaccinating My Cat?

The chance of your cat contracting a serious disease is much higher than the chance of your cat developing a vaccine-associated sarcoma. So it's generally recommended to keep vaccines current.

At the same time, veterinarians are taking every precaution to help reduce the risks associated with vaccines, including:

Eliminating unnecessary vaccines:

If your cat is indoor only and is never exposed to other cats, it may not be necessary for your cat to receive certain vaccines.

Reducing the number of vaccines given in a single location:

Multiple vaccines in one location may induce inflammation, so different vaccines are generally given in different areas of the body. There are standardized locations where each vaccine should be given that help veterinarians determine which vaccines are more likely to produce a problem.

Injecting vaccines in the limbs:

In the past, vaccines were commonly given between the shoulder blades. However, tumors that occur there are difficult to remove. If an aggressive tumor develops in a limb, complete removal (which may include amputation of the leg) is more likely, which can save the life of a cat.

Extending the interval between vaccinations:

Some vaccines are available that last for up to three years, eliminating the need for annual vaccination.

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