Changing distribution of primary cancers in the large bowel.

Analysis of the changing distribution of origin site of 1,990 colorectal cancers observed at a large midwestern hospital shows a statistically significant trend of a decreasing percentage of distal (rectum, P=.0192) and an increasing percentage of proximal (cecum, P=.0015) large-bowel lesions during a period of at least 30 years. Mortality data for 11,635 colorectal cancers in the state of Kansas for this period confirm this trend (P less than .0001). The respective decrease and increase may well be the result of more than one factor. Results of digital examination of the rectum and sigmoidoscopy are less likely to diagnose large-bowel cancer as they did 30 years ago. Stool screening for occult blood, barium enema roentgenographic examination, and colonoscopy become more important diagnostic tools in light of this trend.