Survival improvement in patients with medullary thyroid carcinoma who undergo pretargeted anti-carcinoembryonic-antigen radioimmunotherapy: a collaborative study with the French Endocrine Tumor Group.

PURPOSE: No effective therapy is currently available for the management of patients with metastatic medullary thyroid carcinoma (MTC). The efficacy of pretargeted radioimmunotherapy (pRAIT) with bispecific monoclonal antibody (BsMAb) and a iodine-131 (131I) -labeled bivalent hapten is evaluated. PATIENTS AND METHODS: Twenty-nine patients with advanced, progressive MTC, as documented by short serum calcitonin doubling times (Ct DTs), received an anti-carcinoembryonic antigen (CEA)/anti-diethylenetriamine pentaacetic acid (DTPA) -indium BsMAb, followed 4 days later by a 131I-labeled bivalent hapten. Overall survival (OS) was compared with 39 contemporaneous untreated MTC patients with comparable prognostic indicators.
RESULTS: OS was significantly longer in high-risk, treated patients (Ct DT < 2 years) than in high-risk, untreated patients (median OS, 110 v 61 months; P < .030). Forty-seven percent of patients, defined as biologic responders by a more than 100% increase in CtDT, experienced significantly longer survival than nonresponders (median OS, 159 v 109 months; P < .035) and untreated patients (median OS, 159 v 61 months; P < .010). Treated patients with bone/bone-marrow disease had a longer survival than patients without such involvement (10-year OS, 83% v 14%; P < .023). Toxicity was mainly hematologic and related to bone/bone-marrow tumor spread.
CONCLUSION: pRAIT against CEA induced long-term disease stabilization and a significantly longer survival in high-risk patients with Ct DTs less than 2 years, compared with similarly high-risk, untreated patients. Ct DT and bone-marrow involvement appear to be prognostic indicators in MTC patients who undergo pRAIT.