Update on Vaccine-Associated Sarcoma

Vaccine-associated feline sarcoma probably should be renamed "injection site sarcoma", because these tumors have also been linked to administration of products other than vaccines (eg, dexamethasone and amoxicillin), according to Dr. Barbara Kitchell, University of Illinois. At the AAHA convention, she updated listeners on the latest information gathered by the Vaccine-Associated Feline Sarcoma Task Force. Such information included prevalence, latency period, possible causes, chances of metastasis, and treatment of the disease.

The latency period can vary from three months to three years, the most recent report of prevalence is approximately 5 in 10,000 vaccinated cats, and yes, the tumors are capable of metastasis via the blood to the lungs. Ten to twenty-five percent of these tumors become metastatic after one year. "Tumor(s)" is correct, because the histopathologic diagnosis can vary --fibrosarcoma, malignant fibrous histiocytoma, osteosarcoma, chondrosarcoma, liposarcoma, rhabdomyosarcoma, and anaplastic sarcoma--any connective-tissue tumor can be associated with this syndrome.

One of the most interesting subjects discussed was why the feline species appears to have been singled out for this affliction (actually, other species have been affected, but not to the extent that felids have). Is there a connection between this species, which down through the ages, has incorporated, into their DNA, retroviral elements that are transmitted vertically? Does this mean that a genetic predisposition exists, and is the variable latency period after an injection related to this?

In addition to the retroviral DNA incorporation and potential genetic predisposition, other factors that might account for this syndrome targeting cats include possible tumor suppressor gene p53 mutation and the effect of feline histocompatibility antigens. In this scenario, the vaccine is considered a co-factor in development of the disease.

Also under etiologic consideration are the vaccine factors themselves. In addition to the antigens and adjuvants (which have not been associated with development of the tumor in every instance) contained in the vaccine are other variables that require investigation. These include chemicals added to inactivate the virus, viral contaminants, and cell culture factors (epidermal growth factor, fetal bovine serum, and others) used in manufacture of the product. Regarding the cell culture factors, the injection itself causes and inflammatory reaction in which growth factors similar to those used in vaccine production are released in the cat (eg, platelet-derived growth factor).

With regard to treatment, wide surgical excision is the accepted method, followed by radiation and chemotherapy with carboplatin or other agents if necessary. Controversy exists about when to intervene surgically : at first observation of the lump, when it is in the granuloma stage? or after a biopsy specimen has been diagnosed as malignant?

Many considerations need to be further investigated, Dr. Kitchen said. It is known that FeLV and FIV status are not associated with development of the tumors and that increased risk is associated with increased number of injections and with use of the multiple vaccines. The general hypothesis is that certain genes may be involved, such as (excess mutation of) the p53 gene and the sis (simian sarcoma virus) oncogene that is associated with platelet-derived growth factor. It is obvious that prevention of the disease is of paramount importance, but any bit of information that will lead to an understanding of why and how these tumors develop is useful. Members of the task force are intent on pursuing all avenues of investigation to solve this growing problem in cats.

Dr. Nancy W. Levque

JAVMA, Vol 212, No. 9, May 1, 1998

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