CA-50 as a tumour marker for monitoring colorectal cancer: antigen rises in patients postoperatively precede clinical manifestations of recurrence.

Using a monoclonal antibody-based radioimmunoassay inhibition method we have determined preoperative serum levels of the carcinoma-associated carbohydrate antigen CA-50 in 266 patients with primary colorectal cancer. CA-50 levels exceeding the mean value for blood donor sera by more than 2 standard deviations (greater than or equal to 17 U/ml) were found in 47% of these patients, with 15%, 43% and 31% being elevated in patients with Dukes' A, Dukes' B and Dukes' C cancer, respectively, and 63% and 66% being elevated in patients with more advanced localized or disseminated cancer. Only 5% of patients with benign colorectal disease had elevated CA-50 level and these were patients with ulcerative colitis of a duration of more than 10 years. Among patients who had developed a recurrence after operation for a primary Dukes' A-C colorectal cancer 66% had elevated levels, and 25% of resected patients with no clinical evidence of disease at corresponding times after operation also had CA-50 levels above the normal concentrations. From 139 patients operated for a Dukes' A-C colorectal cancer a definitive rise in CA-50 levels from the pre- to a 6-9 months postoperative sample was demonstrated in 12 cases in the absence of any clinical evidence for a recurrence. On prolonged follow-up a clinically manifest recurrence later developed in all of these cases with lead times of CA-50 titre rises ranging from 5 to 40 months. Our findings suggest that a rise in CA-50 levels after resection of a Dukes' A-C primary colorectal cancer is indicative of a recurrence and may precede any clinical evidence of disease by many months or years. Thus CA-50 may be a clinically useful tool for monitoring of patients with colorectal cancer.