Anti-CEA Pretargeted Immuno-PET Shows Higher Sensitivity Than DOPA PET/CT in Detecting Relapsing Metastatic Medullary Thyroid Carcinoma: Post Hoc Analysis of the iPET-MTC Study
Caroline Bodet‐Milin, Alain Faivre-Chauvet, Thomas Carlier, C. Ansquer, A. Rauscher, Éric Frampas, Frédérique Toulgoat, Damien Masson, Mickaël Bourgeois, Evelyne Cerato, V. Rohmer, Olivier Couturier, D. Drui, David M. Goldenberg, Robert M. Sharkey, Jacques Barbet, Françoise Kraeber‐Bodéré
Abstract
Pretargeting parameters for the use of anti–carcinoembryonic antigen (CEA) bispecific monoclonal antibody TF2 and the <sup>68</sup>Ga-labeled IMP288 peptide for immuno-PET have been optimized in a first-in-humans study performed on medullary thyroid carcinoma (MTC) patients (the iPET-MTC study). The aim of this post hoc analysis was to determine the sensitivity of immuno-PET in relapsing MTC patients, in comparison with conventional imaging and <sup>18</sup>F-l-dihydroxyphenylalanine (<sup>18</sup>F-DOPA) PET/CT. <b>Methods:</b> Twenty-five studies were analyzed in 22 patients. All patients underwent immuno-PET 1 and 2 h after <sup>68</sup>Ga-IMP288 injection pretargeted by TF2, in addition to neck, thoracic, abdominal, and pelvic CT; bone and liver MRI; and <sup>18</sup>F-DOPA PET/CT. The gold standard was histology or confirmation by one other imaging method or by imaging follow-up. <b>Results:</b> In total, 190 lesions were confirmed by the gold standard: 89 in lymph nodes, 14 in lungs, 46 in liver, 37 in bone, and 4 in other sites (subcutaneous tissue, heart, brain, and pancreas). The number of abnormal foci detected by immuno-PET was 210. Among these, 174 (83%) were confirmed as true-positive by the gold standard. Immuno-PET showed a higher overall sensitivity (92%) than <sup>18</sup>F-DOPA PET/CT (65%). Regarding metastatic sites, immuno-PET had a higher sensitivity than CT, <sup>18</sup>F-DOPA PET/CT, or MRI for lymph nodes (98% vs. 83% for CT and 70% for <sup>18</sup>F-DOPA PET/CT), liver (98% vs. 87% for CT, 65% for <sup>18</sup>F-DOPA PET/CT, and 89% for MRI), and bone (92% vs. 64% for <sup>18</sup>F-DOPA PET/CT and 86% for MRI), whereas sensitivity was lower for lung metastases (29% vs. 100% for CT and 14% for <sup>18</sup>F-DOPA PET/CT). Tumor SUV<sub>max</sub> at 60 min ranged from 1.2 to 59.0, with intra- and interpatient variability. <b>Conclusion:</b> This post hoc study demonstrates that anti–carcinoembryonic antigen immuno-PET is an effective procedure for detecting metastatic MTC lesions. Immuno-PET showed a higher overall sensitivity than <sup>18</sup>F-DOPA PET/CT for disclosing metastases, except for the lung, where CT remains the most effective examination.