Patient characteristics, first-line treatments, and overall survival among locally advanced, unresectable or metastatic gastric and gastroesophageal junction adenocarcinoma patients at a large academic medical center in the United States.

317 Background: Patients diagnosed with advanced-stage gastric and gastroesophageal junction cancer (adv GC/GEJC) represent a high-risk population for disease-related morbidity and mortality. This study aimed to describe the patient and clinical characteristics, treatment patterns and survival of those diagnosed with adv GC/GEJC in a US real world setting. Methods: Adult patients diagnosed at MD Anderson Cancer Center with adv GC/GEJC between 01 Jan 2019 and 30 Dec 2023 were identified. Patients with at least one primary or metastatic tumor sample obtained prior to treatment, but within 60 days of diagnosis, for their adv GC/GEJC were included in the analytic cohort. Clinical information and clinically tested biomarkers were obtained from the patient electronic health records. Non-clinically tested biomarkers, FGFR2b (VENTANA FPR2-D) and CLDN18 (VENTANA 43-14A), were measured via immunohistochemistry using archival tumor tissue samples. FGFR2b was assessed as percentage of tumor cells exhibiting moderate (2+) to strong (3+) membranous staining. CLDN18 positivity was defined as >75% of viable tumor cells exhibiting moderate to strong membranous staining. Real-world overall survival (rwOS) was assessed among patients receiving treatment, beginning at date of first treatment until death or last follow-up. Results: Among the 292 adv GC/GEJC patients, the median age at diagnosis was 64 years. The majority were male (77%), white (80%), had GEJC (70%), had an ECOG of 0-1 (84%), and were diagnosed at metastatic disease (88%). Biomarker prevalences from clinical care ranged from 3% to 66%; 3% (n=8/240) of patients were MSI high, 21% (n=58/271) were HER2+, and 66% (n=120/181) had a PD-L1 CPS score ≥5. For biomarkers not tested in clinical care, 12 tissue samples expressed FGFR2b at ≥10% 2+/3+ staining, and 94 were CLDN18 positive. Nearly half (47%, n=137/292) of patients received immunotherapy with or without other medications, followed by chemotherapy alone (20%, n=58/292) and HER2 targeted therapy with or without other systemic therapies (14%, n=40/292). The median rwOS among patients receiving any treatment (n=246) was 13.3 months (95% confidence interval: 12.6, 14.8 months). Regimen-specific median rwOS ranged from 8.2 months in those receiving chemotherapy alone, to 14.7 and 14.4 months among those receiving any HER2 targeted therapy and any immunotherapy, with or without other medications, respectively. Conclusions: These results from the US continue to highlight the poor prognosis for patients diagnosed with advanced-stage gastric cancer, despite recent advances in therapeutic options and biomarker testing. More research is needed to better understand the role of emerging biomarkers in optimizing treatment options and improving patient outcomes.