Molecular features influencing clinical outcome of advanced HER2-positive gastric cancer receiving trastuzumab plus chemotherapy.

[BACKGROUND] Less than half of the human epidermal growth factor receptor 2 (HER2)-positive gastric cancer (GC) patients respond to trastuzumab plus chemotherapy, and the outcomes are unsatisfactory. Understanding the underlying mechanisms remains crucial for identifying patients who are more likely to benefit from treatment.

[PATIENTS AND METHODS] We performed targeted DNA sequencing on paired pre-treatment and progressive tumour tissues from 22 HER2-positive advanced GC patients undergoing first-line treatment with trastuzumab and chemotherapy. Clinicopathological and genomic characteristics were assessed for the correlation with clinical outcomes.

[RESULTS] A performance status (PS) of 0-1 was associated with improved progression-free survival (PFS) and overall survival (OS) than a PS of 2. Poorly differentiated tumours exhibited shorter PFS than moderate or moderate-poor ones. Pre-treatment amplification of or gene was association with increased PFS, and suggested a potential benefit for OS. Patients with higher tumour mutation burden (TMB) experienced significantly worse PFS, while higher chromosome instability (CIN) appeared to be correlated with longer PFS. Compared to non-responders, responders had a higher CIN but similar TMB and intratumoural heterogeneity (ITH). PS and amplification emerged as independent factors related to PFS according to multivariate survival analysis. Additionally, after treatment, TMB significantly increased in non-responders, while CIN significantly decreased in responders.

[CONCLUSIONS] Pre-treatment amplification and PS were independently associated with clinical outcomes in HER2-positive advanced GC patients treated with first-line trastuzumab plus chemotherapy. Dynamic post-treatment changes in TMB and CIS provide valuable insights into the relationship between therapeutic response and distinct evolutionary trajectories.