Distinct age-related effects of homologous recombination deficiency on genomic profiling and treatment efficacy in gastric cancer.

[BACKGROUND] The incidence of gastric cancer among younger patients is increasing globally, with growing attention being paid to the role of homologous recombination deficiency (HRD). However, the effect of HRD on treatment outcomes and prognosis in this population remains unclear.

[METHODS] We analyzed clinical and genomic data from the Center for Cancer Genomics and Advanced Therapeutics database. Younger patients (≤ 39 years, n = 140) were compared with older patients (≥ 65 years, n = 1118) diagnosed with gastric cancer. This study focused on mutations in homologous recombination repair (HRR) genes and their association with tumor mutation burden (TMB), microsatellite instability (MSI), and treatment outcomes.

[RESULTS] In older patients, HRD was associated with higher TMB and microsatellite instability-high (MSI-H) status, whereas no such correlations were observed in younger patients. Notably, MSI-H status was not observed in the younger group. Younger patients with HRD had a significantly shorter time to treatment failure (TTF) and overall survival (OS) than those without HRD. Conversely, in older patients, there was no significant difference in TTF or OS based on HRD status.

[CONCLUSION] HRR gene mutations influence genomic profiling, TMB, and MSI differently depending on the age of gastric cancer onset, suggesting potential effects on treatment efficacy and prognosis.