Promising clinical performance of pretargeted immuno-PET with anti-CEA bispecific antibody and gallium-68-labelled IMP-288 peptide for imaging colorectal cancer metastases: a pilot study

Introduction: This pilot study evaluated the imaging performance of pretargeted immunological positron emission tomography (immuno-PET) using an anti-carcinoembryonic antigen (CEA) recombinant bispecific monoclonal antibody (BsMAb), TF2 and the [68Ga]Ga-labelled HSG peptide, IMP288, in patients with metastatic colorectal carcinoma (CRC). Patients and methods: Patients requiring diagnostic workup of CRC metastases or in case of elevated CEA for surveillance were prospectively studied. They had to present with elevated CEA serum titre or positive CEA tumour staining by immunohistochemistry of a previous biopsy or surgical specimen. All patients underwent endoscopic ultrasound (EUS), chest-abdominal-pelvic computed tomography (CT), abdominal magnetic resonance imaging (MRI) and positron emission tomography using [18F]fluorodeoxyglucose (FDG-PET). For immuno-PET, patients received intravenously 120 nmol of TF2 followed 30 h later by 150 MBq of [68Ga]Ga-labelled IMP288, both I.V. The gold standard was histology and imaging after 6-month follow-up. Results: Eleven patients were included. No adverse effects were reported after BsMAb and peptide injections. In a per-patient analysis, immuno-PET was positive in 9/11 patients. On a per-lesion analysis, 12 of 14 lesions were positive with immuno-PET. Median SUVmax, MTV and TLG were 7.65 [3.98-13.94, SD 3.37], 8.63 cm3 [1.98-46.64; SD 14.83] and 37.90 cm3 [8.07-127.5; SD 43.47] respectively for immuno-PET lesions. Based on a per-lesion analysis, the sensitivity, specificity, positive-predictive value and negative-predictive value were, respectively, 82%, 25%, 82% and 25% for the combination of EUS/CT/MRI; 76%, 67%, 87% and 33% for FDG-PET; and 88%, 100%, 100% and 67% for immuno-PET. Immuno-PET had an impact on management in 2 patients. Conclusion: This pilot study showed that pretargeted immuno-PET using anti-CEA/anti-IMP288 BsMAb and a [68Ga]Ga-labelled hapten was safe and feasible, with promising diagnostic performance.