P-244 Feasibility, safety, and biodistribution of 18F-BMS-986229 PET in patients with esophagogastric (EG) cancer

The addition of programmed cell death protein 1 (PD-1) blockade to combination cytotoxic chemotherapy improves overall survival among patients with EG cancer in the frontline metastatic setting. However, due to tumor heterogeneity, PD-L1 expression based on single site biopsies is inadequate to identify those who will derive benefit from the addition of checkpoint blockade, and better biomarkers are needed. We developed PD-L1 specific positron emission tomography (PET) imaging using 18F-BMS-986229 in patients with EG cancer for non-invasive assessment of tumor PD-L1 status. Patients with EG cancer who had a PD-L1 combined positive score (CPS) >1 by immunohistochemistry received one injection of 18F-BMS-986229 (370 MBq), a PD-L1 targeted tracer, and then underwent a whole-body PET/CT (80 mA) 60 minutes post-injection. Ten patients underwent imaging with 18F-BMS-986229 PET, with a median age of 65 years (37 - 81), nine of whom were male and eight of whom had de novo stage IV disease. All 10 patients had adenocarcinoma; four were gastroesophageal junction tumors, three were esophageal, and three were gastric. Median qualifying PD-L1 CPS was 10 (5 - 70). The maximum tumor standardized uptake value (SUV) on 18F-fluorodeoxyglucose (18F-FDG) PET at the time of 18F-BMS-986229 PET ranged from 3.4 to 24.9. Median number of lines of therapy at the time of imaging was one. All ten patients received treatment with PD-1 blockade during their treatment course (seven with pembrolizumab, three with nivolumab). Two patients had received treatment with PD-1 blockade prior to enrollment and one was actively receiving treatment with PD-1 blockade at the time of undergoing the scan. Seven out of 10 (70%) of patients had at least mild tracer uptake at the primary lesion on 18F-BMS-986229 PET and one patient (1/10, 10%) had an adrenal metastasis with uptake on 18F-BMS-986229 PET. Complete results of 18F-BMS-986229 PET findings, including comparison with 18F-FDG PET, will be presented. No clinically significant toxicities or adverse events were observed. PET imaging with a PD-L1 targeted tracer 18F-BMS-986229 is safe and feasible. PD-L1 PET may be an adjunct to discrete biopsies in evaluating EG cancer PD-L1 positivity. Correlation with tumor PD-L1expression and PET uptake is underway and will be presented.