Tumors of the anus (not the anal sac) are most common in male dogs. Benign tumors (perianal adenomas) are hormone dependent and occur most commonly in dogs that have not been castrated. Malignant tumors (sebaceous gland adenocarcinomas) are not hormone dependent. Benign tumors are treated with local tumor removal (surgery/cryosurgery) and castration (to prevent new tumor development). Treatment and outcome of malignant tumors vary depending on tumor size and possible spread to lymph nodes but generally include surgery and possibly radiation therapy.