Vaccine Associated Fibrosarcoma (Cancer)

CANCER FROM VACCINATION?

(WHAT YOU SHOULD KNOW ABOUT
VACCINE-ASSOCIATED FIBROSARCOMA)
(Also called Injection Site Sarcoma)

WHAT IS A FIBROSARCOMA & WHY DO WE THINK VACCINATION MIGHT CAUSE IT?

Fibrosarcomas have been recognized as difficult, deeply rooted tumors of the cat for a very long time. The fibrosarcoma is a tumor which does not usually spread throughout the body in the way we usually think of cancer; instead, it digs in deeply and widely in a localized area. After surgical removal it is notorious for recurring even more aggressively than before.

(Photocredit: Morguefile.com)

These tumors can result spontaneously in either dogs or cats, as can any cancer, or they can be virally induced in cats via the Feline Sarcoma Virus. While spontaneous and viral fibrosarcomas have been described for decades, the potential for vaccination to lead to the formation of these tumors is a relatively new concern. There are still many unanswered questions about how this is actually happening, the role of vaccination, which vaccinations have been implicated, and how serious the risks actually are. What we do know is:

• When local laws change to require rabies vaccination for cats, the incidence of fibrosarcomas increases in that area.
• The most common sites for fibrosarcomas are the area between the shoulder, the lower back & hind limb (areas commonly used for vaccination in the past).
• Hawaiian cats have a reduced incidence of fibrosarcoma (rabies vaccination is not generally performed in Hawaii as the islands have successfully eradicated rabies). Hawaiian cats DO still get fibrosarcomas. At this time, killed virus vaccines such as rabies and feline leukemia virus vaccines have been primarily implicated.
• Fibrosarcomas in areas commonly used for vaccination seem to be more aggressive/malignant than fibrosarcomas in other areas. We think this means that vaccine-induced fibrosarcomas are more malignant than viral or spontaneously occurring fibrosarcomas.
• Fibrosarcoma incidence is extremely rare with different studies reporting an incidence between one in 1000 to one in 10,000 vaccines administered. To put this in perspective, using the traditional vaccination guidelines a cat would receive three vaccines annually during his or her fifteen year lifespan for a total of 45 vaccines, not including the initial kitten series.
• Dogs are so rarely affected by this phenomenon that is considered of no realistic significance. Vaccine-induced fibrosarcomas seem to be a feline problem only.

Despite the extremely low incidence of this problem, the problem is still very serious and the veterinary profession has responded with numerous studies on how vaccines might be related to tumor formation, why is the incidence so low given how many vaccines are given to cats annually, what can be done for prevention.

HOW MIGHT VACCINATION CAUSE CANCER?

It can take as short a time as two months and as long as ten years to develop a vaccine site tumor but most appear within 4 years of the offending injection.. While most (80%) of the tumors that develop are fibrosarcomas, other types of tumors that can develop through this phenomenon include:

• the malignant fibrous histiocytoma
• the osteosarcoma
• the rhabdomyosarcoma
• the liposarcoma
• the chondrosarcoma
• the undifferentiated sarcoma

(All are tumors of either muscle, bone, cartilage or fat)

SHOULD I STILL VACCINATE MY CAT? The answer is still an unequivocal yes. The incidence of these tumors is exceedingly rare relative to the incidence of the diseases which we vaccinate against. Vaccination remains one of the most important aspects of preventive care for cats but now that the vaccine-associated sarcoma has been recognized, some changes have been made in the way cats are vaccinated. For example, vaccinations are made differently now. Instead of the simple modified live versus killed option, we now have recombinant vaccinations which allow a live non-adjuvanted approach to vaccination against diseases like rabies and feline leukemia virus. These are preferentially used over the adjuvanted killed vaccines that have been heavily implicated in sarcoma formation. Some vaccines are administered in a needle-free manner (such as nasally) to avoid creating a depot of vaccine in the muscle and skin tissues. Vaccines are divided into "core vaccines" which all cats should have regardless of their indoor/outdoor lifestyle (rabies and FVRCP distemper vaccines are considered "core") while other vaccines are given depending on the cat's realistic risk of exposure. For a summary of the 2006 vaccinations guidelines for cats from the American Association of Feline Practitioners visit: www.catvets.com/uploads/HTML/VaccineSummary.html

Two recombinant vaccines made by Merial®. (original graphic by marvistavet.com)

SHOULD I STILL VACCINATE MY CAT?

The answer is still an unequivocal yes. The incidence of these tumors is exceedingly rare relative to the incidence of the diseases which we vaccinate against. Vaccination remains one of the most important aspects of preventive care for cats but now that the vaccine-associated sarcoma has been recognized, some changes have been made in the way cats are vaccinated. For example, vaccinations are made differently now. Instead of the simple modified live versus killed option, we now have recombinant vaccinations which allow a live non-adjuvanted approach to vaccination against diseases like rabies and feline leukemia virus. These are preferentially used over the adjuvanted killed vaccines that have been heavily implicated in sarcoma formation. Some vaccines are administered in a needle-free manner (such as nasally) to avoid creating a depot of vaccine in the muscle and skin tissues. Vaccines are divided into "core vaccines" which all cats should have regardless of their indoor/outdoor lifestyle (rabies and FVRCP distemper vaccines are considered "core") while other vaccines are given depending on the cat's realistic risk of exposure.

For a summary of the 2006 vaccinations guidelines for cats from the American Association of Feline Practitioners visit:

www.catvets.com/uploads/HTML/VaccineSummary.html

GUIDELINES FOR VACCINE-ASSOCIATED SARCOMA PREVENTION

Avoid unnecessary vaccination

Be wary of vaccination recommendations that encourage you to vaccinate for every possible disease. Recommendations are highly regional and individualized according to the philosophy of the animal hospital you are visiting and every veterinarian may have a different philosophy but the guidelines developed by the American Veterinary Medical Association, American Association of Feline Practitioners, American Animal Hospital Association, and Vaccine Associated Sarcoma Task Force are a good place to start (see link above).

Detailed records should be kept by the veterinarian indicating the vaccine lot number & type as well as the site of vaccination.

This also helps researchers determine what is occurring with regard to tumor development.

Be aware of lumps forming after vaccination (The "3-2-1" Rule)

Lumps commonly form in the weeks following vaccination due to the immune stimulation and inflammation centered on this area. These lumps are usually normal and do not represent fibrosarcomas (which generally take years to develop, not weeks). If your cat develops one of these lumps under the skin (they are usually noticed by owners 3-4 weeks after vaccination), the lump may be left alone to resolve naturally. If the lump is still present 3 months from the time of vaccination, it should be removed and biopsied. Any lumps greater than 2 cm in diameter (approximately one inch) should be removed no matter how long a time has past since vaccination. Also, any lump should be removed if it is felt to be getting larger rather than smaller one month after its discovery. ("3-2-1" refers to 3 months post vaccine, 2 cm in size, growing bigger after 1 month.)

Sometimes one such lump will break open. This usually means an infection is present and must be treated rather than that a fibrosarcoma has developed. Your veterinarian should be informed of this occurrence and the pet should return for therapy.

 
(original graphic by marvistavet.com)

TREATMENT FOR VACCINE ASSOCIATED FIBROSARCOMAS

Injection site sarcomas can be thought of as being similar to an octopus in structure. There is the "body" that you see but there are also far-reaching "tentacles" that cannot be seen extending far from the visible body of the tumor. For surgery to be successful, a very broad excision is needed and it is necessary to first determine how far the tumor has spread. Chest radiographs are vital for staging and CT scanning, if available, is very helpful in detecting the extent of the invisible tentacles. If CT scanning is not available, 5 cm (approximately 2 inches) should be removed around the visible portion of the tumor in all directions. Basic blood work including a feline leukemia virus test is needed to fully assess the cat for treatment.

Even with aggressive surgery, the tumor recurrence rate is very high (at least 50% by 6 months after surgery). The wider the excision, the longer the time to recurrence and the longer the survival time but the longest survival times include radiotherapy in the treatment of this tumor. While there is controversy whether or not radiation is best done before or after surgery, it seems clear that radiation can double or even triple survival time. When chemotherapy is added in, survival times can be even higher, still.

It should not be surprising that smaller tumors have longer survival periods than larger tumors and there are different tissue types which can help estimate survival time. Expect a referral to an oncologist to be needed to get the best and most up to date treatment plan.

Our goal in creating this web site is to create awareness of an emerging problem in veterinary medicine, not to elicit panic. We believe that intelligent decisions about pet ownership require information and education. We take the prevention guidelines very seriously and hope that all veterinarians will.

To review our hospital's current vaccination recommendations click here.

Page last updated: 10/14/2016