Anti-CEA pretargeted Immuno-PET shows higher sensitivity than DOPA-PET/CT to detect relapsing metastatic medullary thyroid carcinoma: Post- hoc analysis of the iPET-MTC study.

Introduction: Pretargeting parameters for use the anti-CEA (carcinoembryonic antigen) bispecific monoclonal antibody TF2 and the 68Ga-labeled IMP288 peptide (68Ga-IMP288) for Immuno-PET have been optimized in a first-in-human study performed in MTC (medullary thyroid carcinoma (MTC) patients (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 18F-DOPA PET/CT (DOPA-PET/CT). Methods: Twenty-five studies were analyzed in 22 patients. All patients received Immuno-PET 1-h and 2-h after 68Ga-IMP288 injection pretargeted by TF2, in addition to neck-thoracic-abdominal-pelvic computed tomography (CT), bone and liver magnetic resonance imaging (MRI), and DOPA-PET/CT. Gold standard (GS) was histology and/or confirmation by one other imaging method and/or imaging follow-up. Results: 190 lesions were confirmed by the GS: 89 in lymph nodes, 14 in lungs, 46 in liver, 37 in bone, and 4 in other sites (subcutaneous, heart, brain, and pancreas). 210 abnormal foci were detected by Immuno-PET. Among these, 174 (83%) were confirmed as true-positive by the GS. Immuno-PET showed a higher overall sensitivity (92%) than DOPA-PET/CT (65%). Regarding metastatic sites, Immuno-PET had a higher sensitivity than CT, DOPA-PET/CT or MRI for lymph nodes (98% vs 83% for CT and 70% for DOPA-PET/CT), liver (98% vs 87% for CT, 65% DOPA-PET/CT, and 89% for MRI) and bone (92% vs 64% for DOPA-PET/CT and 86% for MRI), whereas sensitivity was lower for lung metastases (29% vs 100% for CT and 14% for DOPA-PET/CT). Tumor SUVmax at 60 min ranged from 1.2 to 59.0 with intra- and inter-patient variability. Conclusion: This post-hoc study demonstrates that anti-CEA immuno-PET is an effective procedure for detecting metastatic MTC lesions. Immuno-PET showed a higher overall sensitivity than DOPA-PET/CT for disclosing metastases, except for the lung, where CT remains the most effective examination.