Feline injection-site sarcoma is a rare but aggressive cancer at vaccination or injection sites. Early recognition and aggressive surgical treatment are welfare-critical.
The welfare outcome of feline injection-site sarcoma depends critically on how early and completely the tumor is excised. FISS tumors have microscopic infiltrations extending far beyond the visible tumor mass, meaning inadequate surgical margins lead to rapid local recurrence. A cat whose FISS is incompletely excised faces multiple recurrences, repeated surgeries, and ultimately a worse outcome than one whose first surgery achieves true clean margins.
Owner education and the 3-2-1 rule provide the framework for early biopsy. Any post-injection lump persisting more than 3 months, growing, or larger than 2cm warrants veterinary assessment and biopsy. Many bumps in these locations are benign reactions, but early biopsy of concerning lesions enables early, welfare-improving intervention when cancer is confirmed.
Best practice treatment involves wide surgical excision (including adjacent muscle layers), adjuvant chemotherapy with doxorubicin, and radiation therapy. This multimodal approach significantly improves median survival compared to surgery alone. Palliative care for advanced or recurrent disease focuses on quality of life maintenance, pain management, and supporting daily activities as long as welfare indicators remain acceptable.