Companion Animals

Cat Injection Site Sarcoma - Recognition and Welfare

Injection site sarcoma (ISS) is a rare but aggressive cancer in cats associated with subcutaneous injections, requiring rapid recognition and specialist treatment.

Key Facts

ISS is estimated to occur in 1 in 10,000-30,000 injections in cats
Vaccines, microchips and long-acting medications have all been implicated
A lump persisting more than 3 weeks post-injection or exceeding 2cm requires immediate biopsy
Surgical treatment requires aggressive wide margins (3-5 cm) to achieve local control
Adjuvant radiotherapy significantly extends survival time after surgery

Welfare Considerations

Injection site sarcoma causes aggressive local invasion and pain. Rapid recognition and specialist oncological management offer the best chance of welfare-positive outcomes for affected cats.

What You Can Do

Monitor any injection site in your cat for lumps persisting beyond 3 weeks
Request biopsy immediately if a post-injection lump exceeds 2cm or continues growing
Seek referral to a veterinary oncologist if ISS is confirmed on biopsy