Colorectal carcinomas: diagnostic implications of their changing frequency and anatomic distribution.

This retrospective review included 1,694 consecutive cases of colorectal carcinoma diagnosed at the University of Chicago Medical Center during a 25-year period (1960 through 1984). The number and percentage of tumors occurring within 7 anatomic segments of the large bowel were determined. The statistical data for a recent 5-year interval were then compared with those of the 2 preceding decades. There was a 10.2% increase in the frequency of cancers originating in the cecum or ascending colon, while rectal and rectosigmoid carcinomas declined by 15.8% during the same study period. These data provide further evidence for a progressive left-to-right shift in cancer distribution within the colon during the past quarter century. Currently, the most proximal and distal 20-25 cm segments of the large bowel (cecum or ascending colon versus rectum and rectosigmoid) each harbor approximately 25% of the tumors. Therefore, the classic medical teaching that over 50% of colorectal cancers would be detectable by digital examination and/or proctosigmoidoscopy is no longer accurate. This documented increase in proximal colon cancers and redistribution of lesions within various large bowel segments indicate the growing importance of barium enema and colonoscopy as the optimal techniques for detection of colorectal neoplasms.