Molecular characterization of ctDNA from Chinese patients with advanced gastric adenocarcinoma reveals actionable alterations for targeted and immune therapy.

Circulating tumor DNA (ctDNA) is considered an ideal sample type for genotyping patients with advanced unresectable cancer to inform treatment decision. It may better capture tumor heterogeneity, especially in gastric adenocarcinoma (GAC). However, there exists little evidence regarding genomic profiling of Chinese advanced GAC patients from ctDNA. Blood samples were obtained from 200 advanced GAC patients. Next-generation sequencing (NGS) was performed on ctDNA using a validated 150-gene panel. Blood tumor mutation burden (bTMB) was calculated according to the NGS results. Blood microsatellite instability (bMSI) status was determined by targeted sequencing of 100 microsatellite loci. One hundred sixty-nine (84.5%) patients carried at least one genomic alteration and 138 (69%) patients had at least one deleterious or likely deleterious alteration (del-alteration). The clonal fraction of del-alterations was higher than that of non-del-alterations (80.1% vs 54.5%, P < 0.0001). The most frequently altered genes were TP53 (38%), LRP1B (20%), MYC (13.5%), ERBB2 (12.5%), and KRAS (11.5%). The alterations were most enriched in the TP53/cell cycle (52%) and the RTK-Ras-MAPK pathway (51.5%). The median bTMB was two (range 0 to 42). Eight patients were identified to be high bMSI, with higher median bTMB than the blood microsatellite stable (bMSS) patients (15 vs 2, P = 0.0062). Patients harboring del-alterations of the DDR pathway had significantly higher percentages of high bTMB and bMSI-H patients than the wild-type subgroup (61.1% vs 6.5%, P < 0.0001; 33.3% vs 1.7%, P = 0.0002). A total of 45.5% cases harbored at least one potentially actionable alteration and one patient achieved complete response after receiving matched targeted therapy. Our study uncovered the molecular characterization of Chinese patients with advanced GAC from ctDNA, including genomic alteration, bTMB, and bMSI status. The findings suggested that targeted NGS-based ctDNA analysis may help inform the clinical decision in advanced GAC. KEY MESSAGES: We report the molecular profiling of the largest Chinese advance stage GACs cohort using a CLIA-certified ctDNA assay. Potentially actionable genomic alterations were identified in 45.5% of patients, suggesting clinical utility for ctDNA NGS in advance stage GACs. There was evidence of clinical benefit in one GAC patient with MET amplification treated with MET inhibitor.