A measurement of the two-dimensional extent of a planar region comprising the superficial or external aspect of one or more colorectal tumors, abnormal growths of tissue resulting from uncontrolled, progressive multiplication of cells and serving no physiological function, which occur in the large intestine, the distal portion of the alimentary canal, especially in the colon and/or rectum, the segment of the large intestine between the cecum and the anal canal.