Nationwide oncologist survey on biomarker integration and evidence-based gastric/GEJ cancer care: Practice patterns and barriers.

e16059 Background: Biomarker (BM) testing is crucial for guiding first-line systemic therapy in advanced/metastatic gastric and gastroesophageal (advanced G/GEJ) cancer. However, the integration of new and established BMs presents evolving challenges for oncology care teams. This nationwide survey assessed oncologists’ current practices, confidence, and identified barriers related to BM testing and management in advanced G/GEJ cancer. Methods: In 2025, a nationwide survey was conducted among 150 oncologists (oncs) in the US. The survey assessed attitudes, practice patterns, and challenges regarding BM testing and BM-directed therapies for patients with advanced G/GEJ cancers. Results: While guidelines recommend BM testing for all patients with advanced G/GEJ cancers, oncs reported an average of 68% (median: 80%, range: 0%-100%) of their advanced G/GEJ cancer patients receive BM testing. Most oncs reported routinely utilizing PD-L1 (95%) and HER2 (75%) to inform first-line treatment selection in advanced G/GEJ cancers; however, less than half routinely tested for CLDN18.2 (48%), NTRK (47%), BRAFV600E (33%), and microsatellite instability or mismatch repair (MSI/MMR) (27%). Interestingly, subgroup analysis showed differences by practice setting: 26% (32/122) of community oncs vs 44% (12/27) of academic oncs reported routinely incorporating MSI/MMR results into treatment selection. Top challenges in integrating BM testing into treatment selection included difficulty determining whether to begin treatment prior to receipt of BM testing results (56%) and optimizing specimen collection for testing (48%). Oncs emphasized that standardizing panel for BM testing (47%) and arranging with pathologists to perform reflex testing (43%) would most improve incorporation of BM testing into clinical workflows. Some challenges were reported more often in community vs academic care: community oncs reported uncertainty choosing between available immune checkpoint inhibitors (ICIs; 45% vs 19% of academic oncs); in CLDN18.2 testing and treatment selection, community oncs reported uncertainty about CLDN18.2 testing protocols (43% vs 22% of academic oncs) and difficulty interpreting test results and applying them to treatment selection (39% vs 19% of academic oncs). Across practice settings, educating or communicating results to patients or care teams was a top reported challenge for integrating CLDN18.2 testing and zolbetuximab (51%), as well as PD-L1 testing and ICIs (41%). Conclusions: This nationwide survey of oncs revealed persistent gaps in BM testing and interpretation to guide treatment selection for advanced G/GEJ cancers. Despite clear guidelines for BM testing, suboptimal testing persists. Standardized testing, clearer protocols, and targeted education are critical to optimize evidence-based, BM-driven care in advanced G/GEJ cancer.