68Ga-SSO-120 PET for Initial Staging of Small Cell Lung Cancer Patients: A Single-Center Retrospective Study

Abstract

PET imaging using the somatostatin receptor 2 (SSTR2) antagonist satoreotide trizoxetan (SSO-120, previously OPS-202) could offer accurate tumor detection and screening for SSTR2-antagonist radionuclide therapy in patients with SSTR2-expressing small cell lung cancer (SCLC). The aim of this single-center study was to investigate tumor uptake and detection rates of ⁶⁸Ga-SSO-120 in comparison to ¹⁸F-FDG PET in the initial staging of SCLC patients. Methods: Patients with newly diagnosed SCLC who underwent additional whole-body ⁶⁸Ga-SSO-120 PET/CT during the initial diagnostic workup were retrospectively included. The mean administered activity was 139 MBq, and the mean uptake time was 60 min. Gold-standard staging ¹⁸F-FDG PET/CT was evaluated if available within 2 wk before or after ⁶⁸Ga-SSO-120 PET if morphologic differences in CT images were absent. ⁶⁸Ga-SSO-120- or ¹⁸F-FDG-positive lesions were reported in 7 anatomic regions (primary tumor, thoracic lymph node metastases, and distant metastases including pleural, contralateral pulmonary, liver, bone, and other) according to the TNM classification for lung cancer (eighth edition). Consensus TNM staging (derived from CT, endobronchial ultrasound-guided transbronchial needle aspiration, PET, and brain MRI) by a clinical tumor board served as the reference standard. Results: Thirty-one patients were included, 12 with limited and 19 with extensive disease according to the Veterans Administration Lung Study Group classification. ⁶⁸Ga-SSO-120-positive tumor was detected in all patients (100%) and in 90 of the 217 evaluated regions (41.5%). Thirteen patients (42.0%) had intense average ⁶⁸Ga-SSO-120 uptake (region-based mean SUV_max ≥ 10); 28 patients (90.3%) had average ⁶⁸Ga-SSO-120 uptake greater than liver uptake (region-based mean peak tumor-to-liver ratio > 1). In 25 patients with evaluable ¹⁸F-FDG PET, primary tumor, thoracic lymph node metastases, and distant metastases were detected in 100%, 92%, and 64%, respectively, of all investigated patients by ⁶⁸Ga-SSO-120 and in 100%, 92%, and 56%, respectively, by ¹⁸F-FDG PET. ⁶⁸Ga-SSO-120 PET detected additional contralateral lymph node, liver, and brain metastases in 1, 1, and 2 patients, respectively (no histopathology available), and ¹⁸F-FDG PET detected additional contralateral lymph node metastases in 3 patients (1 confirmed, 1 systematic endobronchial ultrasound-guided transbronchial needle aspiration-negative, and 1 without available histopathology). None of these differences altered Veterans Administration Lung Study Group staging. The region-based monotonic correlation between ⁶⁸Ga-SSO-120 and ¹⁸F-FDG uptake was low (Spearman ρ = 0.26-0.33). Conclusion: ⁶⁸Ga-SSO-120 PET offers high diagnostic precision with comparable detection rates and additional complementary information to the gold standard, ¹⁸F-FDG PET. Consistent uptake in most patients warrants exploration of SSTR2-directed radionuclide therapy.

Keywords: 68Ga-OPS-202; 68Ga-SSO-120; PET; SCLC; SSTR.