TARGETING AND INITIAL RADIOIMMUNOTHERAPY OF MEDULLARY-THYROID CARCINOMA WITH I-131-LABELED MONOCLONAL-ANTIBODIES TO CARCINOEMBRYONIC ANTIGEN

The targeting potential of I-131-labeled NP-4 and MN-14 anti-CEA (carc inoembryonic antigen) monoclonal antibodies (MAbs) was assessed in 19 patients with metastatic medullary thyroid cancer (MTC). Seventeen of these patients also entered pilot radioimmunotherapy studies with nonm yeloablative doses of I-131-anti-CEA MAbs, Tumor targeting was possibl e in all 19 patients, with an overall lesion sensitivity of 91%, Tumor dosimetry with I-131-MN-14 IgG or F(ab)(2) was very favorable, with t umor doses of 14.3 +/- 8.3 cGy/mCi and tumor:red marrow dose ratios ex ceeding 3:1 for most lesions, Limited antitumor effects lasting up to 26+ months, based on physical exam, tumor markers, computed tomography , or a followup MAb scan, were seen in 5 of 11 assessable patients giv en relatively low doses of I-131-labeled anti-CEA MAbs, We conclude th at anti-CEA MAbs are excellent agents for targeting metastatic MTC, Th e high tumor uptake of the I-131-anti-CEA antibodies and evidence of t umor response in some patients suggest that radioimmunotherapy with ra dioiodinated anti-CEA MAbs may be an effective treatment for MTC, part icularly when the maximum tolerated dose is given alone or in combinat ion with autologous red marrow or peripheral stem cell support.