False-positive elevations of carcinoembryonic antigen in patients with a history of resected colorectal cancer.

Abstract

403 Background: Routine monitoring of carcinoembryonic antigen (CEA) is standard practice in patients with a history of resected colorectal cancer. While it is known that false positive elevations of CEA can occur, the incidence of false positives and the upper limits of false positive elevations have not been previously well characterized. We evaluated these factors retrospectively in a large, single center, 10-year experience. Methods: Computerized medical records of Memorial Sloan-Kettering were searched electronically and then manually confirmed to identify patients who underwent an R0 resection of local-regional colorectal cancer between January, 2003 and December, 2012 and who had a rise in CEA above the normal range after a normal perioperative CEA. CEA elevations were regarded as false-positive if workup failed to identify the source of the CEA with at least 1 year follow up after the CEA first became abnormal. Results: 728 patients were identified who met all inclusion criteria. Of these, 358 patients (49%) were determined to have had a false-positive CEA elevation, 335 patients (46%) had a true-positive CEA elevation indicative of recurrent colorectal cancer, and 35 patients (5%) had a true positive CEA elevation indicative of development of a new, non-colorectal malignancy. Of those with false elevations, 111 had a single isolated CEA elevation (median highest CEA of 5.5ng/ml, range: 5.1-45.2ng/ml) with no further abnormal CEAs, while 247 had CEA elevations on two or more readings with median highest CEA of 6.7 (range: 5.2-34.9ng/ml). Of these 247 patients with confirmed false-positive CEA elevations, only 5 patients (2%) were above 15ng/ml and no confirmed CEA elevation over 35ng/ml was a false positive. Conclusions: False positive CEAs in the 5-15 range are relatively common. Confirmation of CEA elevation in this range prior to initiating imaging studies may be appropriate. False positive CEAs above 15 are rare. In our large data set, all CEAs above 35 were associated with actual cancer recurrence; hence CEA levels above 35 appear to be virtually diagnostic of the presence of cancer.