Carcinoembryonic antigen (CEA): its role as a monitor of radiation therapy for colorectal cancer.

Serial CEA radioimmunoassays have been performed on patients receiving radiation therapy preoperatively or as treatment of recurrent or metastatic colorectal cancer. Pretreatment circulating CEA titers which were elevated showed a significant decrease with accumulating doses of irradiation, indicating that the bulk of CEA-producing tumor was within the radiation therapy portal. The decrease of circulating CEA with preoperative radiation therapy was short-lived and suggested that surgical resection should be performed within 8 weeks of irradiation. Serial CEA titers are useful as an adjunct to other clinical, laboratory and radiologic data in formulating patient management decisions.