Perianal (hepatoid) adenocarcinoma is a malignant tumour arising from the hepatoid glands — specialised sebaceous glands found in the skin around the anus, so named because their cells resemble liver (hepatic) cells under the microscope. It is important to distinguish this malignant tumour from the far more common benign hepatoid adenoma, which occurs predominantly in intact male dogs and often regresses with castration. Unlike the benign form, hepatoid adenocarcinoma does not regress with castration and can occur in either sex. It also differs from anal sac apocrine gland adenocarcinoma, which is a distinct tumour type arising from a different gland. The malignant form can invade locally and spread to regional lymph nodes. Treatment is primarily surgical, and prognosis depends on the tumour size, grade, and whether complete excision is achieved.