Cat Sarcoma: Injection Site Reactions and Welfare

Feline injection site sarcoma (FISS) is an aggressive tumor associated with vaccination and other injections. Understanding the risks and management options is essential for affected cats.

Key Facts

FISS develops in approximately 1-4 per 10,000 cats vaccinated and is highly aggressive
The tumor develops at the site of vaccination or other injections, typically between the shoulder blades
FISS has a poor prognosis with local recurrence rates of over 50% even after aggressive surgery
Modern vaccination protocols recommend injection sites on the limbs rather than between the shoulder blades
Limb injection sites allow amputation as a more complete surgical option if FISS develops
Vaccine adjuvants have been implicated but the precise causative mechanism is not fully established

Welfare Considerations

FISS causes significant suffering through its aggressive local invasion and high recurrence rate. Surgery for FISS requires wide, deep margins to reduce recurrence risk — often involving major reconstruction. Recurrent tumors further invade vital structures. The welfare burden for affected cats is high, making prevention through vaccination site modification and early detection through lump monitoring genuinely important. Any new lump at a vaccination site warrants urgent veterinary assessment.

What You Can Do

Report any new lump at a vaccination site to your vet promptly — especially if it persists beyond 3 months or is over 2cm
Ensure your vet uses limb vaccination sites (rear leg or tail base) rather than between the shoulder blades
Follow the current vaccination schedule recommended for your cat — vaccination benefits outweigh FISS risk
Pursue aggressive surgery with wide margins if FISS is confirmed — partial surgery leads to rapid recurrence
Consider referral to a specialist veterinary oncologist for FISS management
Discuss adjuvant therapies including radiation and chemotherapy with your oncologist for complete care