[Colorectal cancer and synchronous adenomatous or malignant polyps--factors influencing its incidence].

A retrospective study was made of 433 patients with colorectal cancer who were operated on between January, 1971 and September, 1986. Two-hundred and forty-eight synchronous polyps (226 adenomas and 22 carcinomas) were found in 128 patients (29.6%). The incidence of polyps varied according to the patient's age, sex, family history of colorectal cancer, and also according to the macroscopic classification, depth of infiltration, and the number of the primary tumors. Of these, macroscopic classification seemed to be the most important factor determined by multivariate analysis. The incidence of synchronous polyps of the protuberant type were the highest (50%), as compared to the ulcerating type (28%) and the infiltrating type (19%) (p less than 0.03).