Dogs: Mammary tumours are common in intact females. About half are malignant overall;

Outcome varies by tumour type, size, grade, and lymph-node status.

Surgery cures many dogs when the tumour is small, fully removed, and hasn’t spread.

 

Cats: Mammary tumours are usually malignant (carcinomas) and behave aggressively.

Best results come from early, wide surgical removal of the entire affected chain (radical mastectomy), sometimes staged on both sides. Prevention matters: Spaying before first heat slashes lifetime risk in dogs (≈0.5% if spayed before the first heat vs 8% after one heat, 26% after two).

In cats, spaying before 6 months cuts risk by about 91%, and before 1 year by 86%.