Increased risk of colorectal cancer following breast cancer.

Identification of population groups at increased risk for colorectal cancer is important for deriving maximum benefit from screening procedures. A retrospective analysis of 7605 patients with cancer treated between 1958 to 1982 revealed that the colorectum was the site of metachronous primary in 38 patients (15 males and 23 females). The risk factor of developing the metachronous multiple primary cancer was determined by comparing the observed number of second primary malignancy with the expected number based on person years of observation, age, sex, and site specific incidence rates. Incidence of metachronous colonic cancer was twice the expected number and was the highest following a primary in the breast. This increased risk (2.0) is of equal magnitude as noted following primary colon cancer (1.7). Advanced metachronous colonic lesions were seen more often following breast cancer than following colon cancer. Since carcinoma of the breast is the leading cancer in women, it is urged that the follow-up management of such patients include the same aggressive screening program as that recommended for those with colorectal cancer.