Vaccine-Associated Sarcomas in the Cat

One of the greatest concerns of all pet owners is the thought of cancer affecting their pet. Lately, pet owners have become aware, and justifiably concerned, about a condition called feline vaccine-associated sarcoma. 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. This critical issue is of great concern to both practitioners and the cat owner and has lead to the creation of a professional organization (Vaccine-Associated Feline Sarcoma Task Force), new research on vaccines and vaccine recommendations, and a wealth of information from experts in the area of feline oncology on how to detect these tumors and treat them successfully. The purpose of this article is to provide the cat owner with a general overview of the information available on vaccine-associated sarcomas. Hopefully, an owner knowledgeable on how these tumors develop and how they are diagnosed and treated will be better able to make comfortable and accurate decisions about their cats health plan.

Vaccine-associated sarcomas are soft tissue tumors (they form in muscle, skin and connective tissue) which are found at or near the site of a previous vaccination. Because most vaccines are administered in the interscapular area (between the shoulder blades) at the back of the neck, this is where the tumors are almost always often found. The vaccines that are most often associated with sarcoma development are the Feline Leukemia vaccine, and to a lesser degree the Rabies vaccine. Although there are a few known instances of sarcomas that have developed from injections that were not vaccines, it is rare. According to research from Mattie J. Hendrick and the University of Pennsylvania, "persistent inflammation or wound healing, or both, associated with vaccine components leads to proliferation of fibroblasts and myofibroblasts [fiber and muscle growing cells] that undergo neoplastic transformation [the growth of cancer] through unknown mechanisms." It must be noted that the use of a dull needle might also increase the likeliness of inflammation and is therefore discouraged. Most feline practitioners also use vaccines that come in a single dose vial, therefore minimizing the chances of any contamination that could also lead to inflammation at the injection site. An intensive amount of research is currently being devoted to developing less reactive vaccines and veterinarians are adopting new vaccination protocols to prevent sarcoma formation.

Tumors have been noted in both male and female cats, and although they are more common in middle-aged to older cats, they can be found in young cats as well (which is not typical for most types of cancer). According to Colorado State veterinary oncologist Gregory Ogilvie "vaccine/injection associated malignancies have been reported to develop within weeks to years after injectionthe more often a cat is vaccinated, the higher the risk of vaccine-associated sarcomas." Therefore, an older cat that has received a lifetime of vaccines is a more likely candidate for a vaccine induced tumor.

Once the owner notes a lump in the area where vaccines are administered, it is imperative to seek veterinary care immediately. As Dr. Ogilvie notes "a definitive procedure cannot be planned and the client cannot be informed of the potential risks and benefits of these procedures unless the identity of the tumor is obtained, the extent of the primary and or metastatic disease (the emergence of the cancer in other areas of the body), is elucidated, and the condition of the patient is documented." Because of the aggressive nature of these tumors, the diagnosis and treatment is complex, and how the patient is treated initially may have a great bearing on the outcome of each case. Once the veterinarian has confirmed that the lump may be a tumor (versus an abscess, foreign body, granuloma, fatty deposit, or other benign event) the next step is to obtain tissue by a fine needle aspirate or biopsy. This tissue sample should be sent to a clinical pathologist/oncologist to review for a definitive diagnosis. Once the diagnosis of sarcoma is made (or any other diagnosis of this type of malignant tumor) the next step is to determine if there is metastatic disease. Radiographs (or x-rays) should be taken of the chest and the area of the tumor. This will help show any spread of the disease to the lymph nodes or to the lungs, the two most common sites for metastasis, or spreading, of the tumor. Any lymph nodes that are enlarged should be biopsied as well. Ideally, computerized tomography (CT), magnetic resonance imaging (MRI), or diagnostic ultrasonography should be used to determine the extent of the primary tumor. However, these diagnostic tools are not available to the average feline practitioner and usually require a visit to a private referral institution or one of the university veterinary teaching hospitals.

The general health of the patient must be assessed as well. A complete blood count, general chemistry profile, urinalysis, thyroid assessment, feline leukemia, and feline immunodeficiency virus tests should all be run by the veterinarian. These tests allow the practitioner to get an accurate assessment of the patients overall health and will help determine the treatment and prognosis for any cat afflicted with sarcoma. More importantly, these diagnostic tests give the client information that they will need to make the appropriate decisions regarding the care of their pet and what the benefits of treatment may offer them.

Small- to medium-sized confirmed sarcomas are usually treated with surgical excision. Extra tissue around the tumor is also removed as well to ensue that all cancerous cells are excised. According to Dr. Ogilvie "computerized tomography and magnetic resonance imaging are often a valuable tool to help direct the tumor excision. Adjunctive therapy with radiation and chemotherapy are often recommended." However, as noted before, these therapies, while ideal, are only available at referral institutions and therefore may not be accessible to all clients. There has been some research on the use of immune stimulants to control the growth of these tumors, but because of the lack of scientific data proving their efficacy, surgical excision remains the initial treatment of choice for small to medium sized tumors. With complete excision alone the prognosis for recovery is good if the patient is in fair health and there is no noted metastasis. With radiation and chemotherapy the chances for survival increase.

Large tumors that cannot be treated surgically initially are of greater concern. These tumors may encompass large amounts of soft tissue or bone and may need to be reduced in size with chemotherapy or radiation before they can be surgically removed. These tumors carry a much worse prognosis. It is often difficult, because of the invasive nature of sarcomas, to remove all of the cancerous material from the cat, and therefore recurrence is much more likely.

The initial period after surgery and/or radiation and chemotherapy treatment can be a very difficult time for the patient. Postoperative pain control is used judiciously for the first few days to keep the cat comfortable. The incision must be kept clean and dry and the cat must be monitored closely for any signs of fever, swelling, or discharge. Common adverse affects from radiation can be hair loss or change in hair or skin color. The most common side effects from chemotherapy are inappetance (loss of appetite) and nausea. Although medications can be given to control vomiting, the patient must be monitored carefully for dehydration and weight loss.

Each client must carefully consider the prognosis his or her cat has for long term survival when deciding to undergo treatment for sarcoma. Often, the average time of survival before recurrence of the tumor can be limited to just a few months. There are some animals that have survived greater than two years after treatment, but most had radical surgical excisions and were treated at a referral institution with radiation and chemotherapy. The decision to treat must be made after considering each patients specific condition. The expense, emotional toll on the owner, comfort of the patient, and the prognosis for survival must all be considered.