Adenomatous polyps and carcinoma in situ of the canine colon and rectum: 34 cases (1982-1994).

The medical records of 34 dogs (median age, eight years) with colorectal mucosal lesions were reviewed. Hematochezia was the most common (82%) presenting sign. Most dogs (79%) presented with solitary masses located in the rectum. After histological review, 12 masses were classified as adenomatous polyps and 22 as carcinoma in situ. Recurrence of clinical signs were common (41%), and malignant transformation of the tumor was documented in 18% of the cases. A higher recurrence rate and malignant transformation occurred in dogs presented with multiple masses or diffuse disease and in dogs initially diagnosed with carcinoma in situ.