Colon and rectal carcinoma: spatial distribution and detection.

Recent studies have challenged the concept that 50% of colon cancers are detectable by digital examination and two-thirds are within reach of the rigid sigmoidoscope. This is an important consideration because of the potential for failure of an otherwise appropriate screening method when evaluating a patient for carcinoma of the colon. An analysis of 2,298 cases of colorectal carcinoma diagnosed over 20 years showed that the most common sites were the rectum (34%) and sigmoid (25%). Over the 20 years, the incidence of cancer in the cecum increased and that in the rectum decreased. Cecal, ascending, and transverse colon cancers accounted for 34% of lesions - all beyond the range of the flexible sigmoidoscope. The changing site distribution emphasizes the need for an accurate and inexpensive technique to evaluate the entire colon. These data suggest that the barium pneumocolon examination should be included in the screening of high-risk patients.