Efficacy and survival of anti-PD-1 antibody in combination with trastuzumab and chemotherapy versus trastuzumab and chemotherapy as first-line treatment of HER2-positive metastasis gastric adenocarcinoma: a retrospective study

Background: The KEYNOTE-811 study exhibited promising preliminary results for HER2-positive metastasis gastric adenocarcinoma; however, long-term survival benefit remains to be determined.

Methods: In this single-center, controlled, retrospective study, patients with histologically confirmed HER2-positive unresectable or metastatic gastric/gastroesophageal adenocarcinoma received either anti-PD-1 antibody combined with trastuzumab and chemotherapy (cohort A) or trastuzumab and chemotherapy treatment (cohort B). The primary end points were progression-free survival (PFS) and overall survival (OS). The secondary end points were objective response rate (ORR), disease control rate (DCR), and duration of response (DoR).

Results: A total of 56 patients were eligible to join the study, with 30 patients in cohort A and 26 patients in cohort B. The median PFS (mPFS) was 16.2 months (95% CI, 15.093-17.307) in cohort A versus 14.5 months (95% CI, 9.491-19.509) in cohort B (p = 0.58). The median OS in cohort A was 28.1 months (95% CI, 17.625-38.575) versus 31.6 months (95% CI, 13.757-49.443) in cohort B (p = 0.534). ORRs were 66.7% and 50% in the two groups, respectively. DCRs were 90% and 84.6% in the two groups. Median DoR was not reached in cohort A and it was 16.3 (95% CI, 8.453-24.207) months in cohort B (p = 0.141). The most common irAEs were grade 1 hypothyroidism (33.3%) in cohort A. No treatment-related deaths occurred in this study.

Conclusions: This retrospective cohort study provided a preliminary picture on the long-term follow-up of combining anti-PD-1 antibody with trastuzumab and chemotherapy in HER2-positive GC, and a trend with longer DoR and ORR was identified. Further studies with larger sample sizes and more in-depth molecular investigation are needed.