Canine perineal tumours.

One hundred and thirty nine canine perineal tumours were histologically evaluated. The vast majority (134 tumours = 96.4%) appeared to originate from the characteristic glandular structures of this region. They were classified as well differentiated perianal gland tumours (58.3%), as moderately or poorly differentiated perianal gland tumours (21.6%) and as carcinomas without perianal gland differentiation (16.5%). Only 5 tumours (3.6%) appeared to originate from non-characteristic perineal structures. A prominent male predominance was found with respect to the perianal gland tumours, whereas the carcinomas showed a distinct female predisposition. Tumours showing perianal gland differentiation almost invariably will have a benign behaviour. The carcinomas lacking any perianal gland differentiation often show a distinct malignant behaviour with metastases to regional lymph nodes and internal organs. These malignant neoplasms showed morphological and clinical features comparable to canine anal sac gland adenocarcinomas and carcinoids in man and animals.