Prospective studies of laboratory and radiologic tests in the management of colon and rectal cancer patients: I. Selection of useful preoperative tests through an analysis of surgically occult metastases.

The laboratory and radiologic tests that give useful information in colon and rectal cancer patients over and above that obtained by routine work-up and surgical exploration of the abdomen have not been defined previously. An analysis of surgically occult metastases was used to discover which test would assist in the management of these patients. Occult metastases for radiologic tests were those occurring within one year after resection of the primary tumor; for CEA they were metastases occurring at any time following surgery. Full lung tomography, liver/spleen scan, computerized tomogram of the abdomen, intravenous pyelogram, bone scan, and postoperative baseline CEA greater than 2.5 ng/ml were analyzed. The postoperative baseline CEA was the most sensitive test detecting occult metastases in 57 per cent (12 out of 21) of a high risk patient population. Both postoperative baseline CEA and computerized tomograms of the abdomen had high positive predictive values of 71 and 67 per cent. The negative predictive percentage of computerized tomograms of the abdomen (18 per cent) was lower than that of CEA (21 per cent). In comparing these tests in individual patients with occult recurrence, postoperative CEA and computerized tomograms of the abdomen were seen to be complementary in that approximately 90 per cent of occult metastases were detected when both examinations were used. Computerized tomogram of the abdomen and postoperative baseline CEA are useful in patients with primary colorectal cancer as part of their routine work-up.