Feline injection site-associated sarcoma: Is it a reason to critically evaluate our vaccination policies?

Feline injection site-associated sarcoma (FISAS) or vaccination-associated sarcoma is a serious problem in cats because of the ethical and therapeutic consequences associated with the disease. The exact aetiology of FISAS is unclear; therefore, instituting preventative measures such as delaying or discontinuing vaccination schedules is questionable. This paper will give insights into the disease process, will attempt to answer the question, “what causes FISAS?”, and will discuss preventative measures to decrease the chance of occurrence. Tumours are in general uncommon in the cat, however, malignant tumours, such as sarcomas, occur relatively frequently. FISAS have stimulated interest because of their reported linkage to certain types of vaccine. FISASs are reported to have an incidence of 1-10 per 10,000 cats and often appear in conjunction with a traumatic incident (such as a vaccination). The tumour displays an extreme malignant biological behaviour, both being locally aggressive and metastasising in 25-70% of the cases. Although the pathology still remains unclear, an exaggerated inflammatory/granulomatous response seems to be the predisposing factor in the transformation to FISAS. A multi-step carcinogenesis model, including genetic, iatrogenic and local factors seems to be the most plausible explanation for the occurrence of the tumour. Multi-modal therapy, based on aggressive surgical removal of the tumour in combination with radiation and/or chemotherapy, is usually recommended but randomised clinical studies have not yet been performed to prove the efficacy of any of the modalities. The question of whether FISAS can be prevented by not injecting irritant products remains unanswered. No specific brands of vaccine, manufacturers or factors associated with vaccine administration have been significantly associated with FISAS in a multi-institutional and epidemiological study. Control and evaluation measures as recommended by the US-based taskforce include determination of risk groups, extending re-vaccination intervals, the use of single component products and the use of consistent, predetermined sites for vaccination.