IMPROVED DETECTION OF MEDULLARY-THYROID CANCER WITH RADIOLABELED ANTIBODIES TO CARCINOEMBRYONIC ANTIGEN

Purpose: This investigation was undertaken to assess the targeting of established and occult medullary thyroid cancer (MTC) with radiolabele d monoclonal antibodies (MAbs) reactive with carcinoembryonic antigen (CEA). Patients and Methods: Twenty-six assessable patients with known or occult (n = 17) or occult (n = 9) MTC were studied with radiolabel ed anti-CEA MAbs. Scintigraphic images were collected to determine tar geting of tumor lesions. Results: The targeting results of technetium 99m (Tc-99m)-, iodine 123 (I-123)-, and iodine 131 (I-131)-labeled ant i-CEA antibodies (all directed against the same epitope of CEA) indica ted that all these reagents were capable of detecting established and occult MTC. The sensitivity for detection of known sites of disease ra nged from 76% to 100% for the various anti-CEA MAbs used, when compare d with computed tomography (CT), magnetic resonance imaging (MRI), bon e scan, or other imaging modalities. Moreover, the antibody scan was p ositive in seven of nine patients with occult disease (patients with n egative conventional imaging studies, but who had elevated calcitonin and/or CEA levels). Three of seven patients underwent surgery and the disease was confirmed by histopathology in all three. Conclusion: Anti -CEA MAbs are excellent agents for imaging recurrent, residual, or met astatic MTC. The high lesion sensitivity in patients with known lesion s, combined with the ability to detect occult disease, may make these agents ideal for staging patients, monitoring disease pretherapy or po sttherapy, and especially for evaluating patients with recurrent or pe rsistent hypercalcitonemia or CEA elevations after primary surgery. An alogous to radioiodine in the evaluation of patients with differentiat ed thyroid cancer, radiolabeled anti-CEA MAbs may achieve a similar ro le in diagnosing and monitoring patients with MTC. (C) 1996 by America n Society of Clinical Oncology.