My cat has a lump — should I worry?

Finding a lump on your cat is always worth investigating — unlike dogs, where most lumps are benign, cats have a higher proportion of malignant skin tumours and a notoriously quick-growing cancer called injection-site sarcoma.

Common benign lumps in cats

- Sebaceous cysts — blocked skin gland; may discharge waxy material. Benign but can become infected.
- Abscess — a painful, hot, soft lump filled with pus, usually from a cat bite. Common in outdoor cats. Requires antibiotics and often surgical draining.
- Lipoma — uncommon in cats compared to dogs, but they do occur. Soft, moveable, and usually harmless.
- Feline acne — small blackheads or lumps on the chin, sometimes becoming infected pustules.

Lumps that are more concerning in cats

- Mast cell tumours — can appear anywhere on the skin. Variable appearance from a small firm nodule to an ulcerated mass.
- Squamous cell carcinoma (SCC) — common on ears, nose, and eyelids, especially in white or pale-coloured cats exposed to sun. Starts as a red sore that does not heal.
- Injection-site sarcoma (feline injection-site sarcoma, FISS) — an aggressive cancer that can develop weeks to years after a vaccination or injection. Appears as a firm, growing lump between the shoulder blades or in the muscle. If any lump in this area grows larger than 2 cm, grows faster than usual, or persists more than 3 months after an injection, it must be biopsied immediately.

What to expect at the vet

Fine needle aspiration (FNA) is the first step — quick, minimally invasive, and provides a cell sample for analysis. If inconclusive, a biopsy under sedation may be needed.

Do not wait and watch any new lump in a cat. The difference in outcome between early and late diagnosis of feline cancer is dramatic.