Vaccines and Sarcomas: A Concern for Cat Owners

Vaccines can lessen the severity of future diseases and certain vaccines can prevent infection altogether, and today, a variety of vaccines are available for use by veterinarians. Any treatment carries some risk, but these risks should be weighed against the benefits of protecting your pet from potentially fatal diseases. An uncommon but serious adverse reaction that can occur with injection sites, including those sites where vaccines are administered, is tumor growth (sarcomas), which can develop weeks, months, or even years after a vaccination.

Although the risk of feline injection-site sarcomas (FISS) is small, progress has been made over the years to help reduce that risk even further.

Why do I need to vaccinate my kitten/cat?

Vaccines help your cat’s immune system fight infections from disease-causing micro-organisms. Within some or many of these vaccines are killed micro-organisms or parts of microorganisms that will stimulate your cat’s immune system to produce proteins called antibodies so that when your cat encounters the actual living microorganism those antibodies will “fight off “the infection. The vaccine prepares the cat’s immune system to fight subsequent infections much more quickly and efficiently, thus either preventing infection or decreasing the severity of disease.

Kittens are even more susceptible to disease than adult cats because their immune systems are not as well developed. However, maternal antibodies (obtained through their mother’s first milk) help the kitten’s immune system fight disease until they mature and are able to create their own immune response. These antibodies help fight infection but also interfere with vaccination efforts. Thus, vaccines typically need to be administered in a series to ensure adequate coverage.

Every cat faces different infectious challenges depending on age, health status, lifestyle, and environment. This is why it is so important to work with your veterinarian to plan a vaccine protocol that is best for your cat.

What side effects could I typically expect after my cat’s vaccination?

Vaccine side effects commonly happen and can develop within hours of vaccination. Milder side effects include: local swelling and discomfort at vaccination site, mild fever, lethargy and decreased appetite. (See Vaccinations:What to expect after your pets vaccination for more information)

More serious (and less common) side effects include persistent vomiting and diarrhea, itchy and bumpy skin (“hives”), facial swelling, severe difficulty breathing, and collapse. These reactions can be life-threatening and are medical emergencies. Contact us immediately if any of these signs develop.

A small, firm swelling may also develop under the skin at the site of a recent vaccination; this should disappear within a couple weeks. If the swelling persists for more than three weeks, or if it appears to grow larger in size, contact us at Tampa Bay Pet Hospital in Islamabad.

What are feline injection-site sarcomas?

Although rare, feline injection-site sarcomas (FISS) are cancerous tumors that can arise following injections. Because vaccines are among the most common injections cats receive, vaccination is sometimes a concern for pet owners who might have heard about injection-site sarcomas.

While a specific cause has not been established, it is thought that inflammatory processes related to administration of injectable products can lead to formation of sarcomas.The role of adjuvants (including those containing aluminum) and local inflammation in the pathogenesis of FISS is not clear. (An adjuvant is a substance added to the vaccine to increase the effectiveness of the component antigens - such as killed microorganisms - in induction of an immune response.)

Recent studies suggest that vaccines and other injected agents are risk factors for FISS. These studies also show that in some cats the mere process of instilling a substance into the skin can induce inflammation. There is speculation that this inflammation is not controlled in some cats and this might explain how this transforms into a sarcoma. For the vast majority of patients, vaccination is a low risk and no vaccine is known to be completely risk free. It is possible that any injection in the right cat may lead to an injection site sarcoma (studies are underway to determine whether genetics of the cat are a factor). It is important to note that the disease causing organisms themselves are not likely to cause injection-site sarcomas; inflammation associated with the vaccine administration is more likely the concern. Due to their aggressiveness, these tumors can invade local tissue and even metastasize to other areas of the body which can lead to a very poor prognosis.

Injection-site sarcomas are considered to be a rare development. Reports indicate that they occur at a rate of about 1 case per 10,000 to 30,000 vaccinations.

Why should I vaccinate my cat if a sarcoma can develop?

Vaccines are administered to protect cats against diseases they can easily acquire and those that could have fatal consequences if your cat is not protected.Talk with us at Tampa Bay Pet Hospital in Islamabad about which vaccinations are the most important for your cat. The lifestyle of the cat and previous incidence of FISS are  taken into consideration.

My cat has a lump where a vaccine has been given - what do I do now?

Contact your veterinarian if the lump persists for more than three weeks or seems to be getting larger. A small, firm swelling under the skin may develop at the site of recent vaccination and should start to disappear within a couple of weeks.

Why do cats seem to be especially at risk?

While injection site sarcoma has been reported in other animal species, cats seem to have a more aggressive reaction for reasons that have not yet been established. Scientists have not found genetics to play a direct role but research in this area continues.

How long after vaccination can sarcomas develop?

The time interval between vaccine administration and development of a sarcoma can vary tremendously; they have been seen to occur anywhere between 2 months to 10 years after vaccination.

How are sarcomas diagnosed?

Injection-site sarcomas must be differentiated from other types of vaccine associated reactions, which can include mild symptoms such as weakness and fever to the development of hard lumps at the vaccine site after vaccination. Always tell your veterinarian if you cat has any symptoms lasting more than a few days, or your cat has severe signs like trouble breathing.

Varied diagnostic and treatment plans might be needed so your veterinarian at Tampa Bay Pet Hospital in Islamabad can develop treatment options to your pet.

Although advanced imaging (CT, MRI) may not be feasible for all, the AAFP suggests that the best prognosis for these tumors is when advanced imaging is done to determine ideal ways forward. This is because advanced imaging is the best way to know the extent of tumor involvement.

How are injection-site sarcomas treated?

These tumors are typically treated aggressively and quickly. There are various treatment options, including surgery, radiation therapy, and chemotherapy.

Research has shown that aggressive first-time surgery, either before or after definitive radiation therapy is valuable. There are other therapies, such as chemotherapy, that are sometimes used depending on the situation. Many newer more novel therapies are currently being explored.

What’s the prognosis for injection-site sarcomas in cats?

The prognosis is variable. As with most cancers early detection and thus early treatment is most closely related to a good outcome. Yearly check-up examinations of your cat will enable us to discover early lesions before they grow large and become difficult to remove.

Are vaccines safer now?

The USDA and vaccine companies place great emphasis on vaccine safety and continually work to improve the safety profiles of vaccines. In addition, increased research on duration of vaccine immunity has made it possible to avoid over-vaccination and unnecessary risk to the patient. However, it is important to remember that all vaccines carry some risk and no vaccine is 100% safe.

Brought to you by Tampa Bay Pet Hospital and American Veterinary Medical Association.