Carcino-embryonic antigen--no help with the differential diagnosis.

Two patients who were referred because of an increase in serum carcino-embryonic antigen (CEA) were diagnosed after a number of years as having a medullary thyroid carcinoma. The relationship between CEA and medullary thyroid carcinoma is discussed. The serum level of CEA is neither sensitive nor specific enough to serve as a diagnostic tool. Its determination, however, is useful in the follow-up of patients with carcinoma of the breast, colo-rectal carcinoma and medullary thyroid carcinoma.