Synchronous and metachronous malignancies of the colon and rectum.

In a brief survey of the literature on colorectal malignancy, the incidence of multiple primary (synchronous and metachronous) malignancies is reviewed. A changing pattern of incidence is noted, with decrease in incidence of rectal malignancies and increasing incidence of colonic malignancies, especially in the right colon. The author recommends stool screening for blood and more roentgenographic and endoscopic studies of the colon for earlier diagnosis of colonic malignancies.