Objective To evaluate the relationship of early tumor shrinkage and depth of tumor response with the clinical efficacy and prognosis of programmed death-1 (PD-1) inhibitor combined with trastuzumab and first-line chemotherapy in the treatment of HER-2-positive advanced gastric cancer.

Methods We retrospectively analyzed data from 40 patients treated with this combination at Nanjing Drum Tower Hospital, The Affliated Hospital of Nanjing University Medical School from June 2018 to March 2023. Key metrics included early tumor shrinkage (ETS), depth of response (DpR), objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and adverse reactions. Survival analysis using Log-rank test and Kaplan-Meier method, and plot PFS and OS survival curves. COX regression analysis for correlation testing.

Results The patient's ORR was 77.5%, DCR was 100%, complete response rate was 15.0%, median PFS (mPFS) was 11.10 months, and median OS (mOS) was 30.77 months. COX univariate analysis showed that tumor differentiation, liver metastasis, distant lymph node metastasis, DpR were related to PFS and OS (all P<0.05), ETS was only related to PFS (P=0.010), and PD-L1 expression was not related to PFS and OS. There was a significant difference in mPFS between patients with ETS≥35% and ETS<35% (P=0.008), while there was no significant difference in mOS (P=0.076); There were significant differences in mPFS and mOS between patients with DpR≥40% and DpR<40% (P=0.001). COX multivariate analysis showed that DpR is an independent factor affecting PFS and OS, and distant lymph node metastasis is an independent factor affecting OS. The overall tolerance to treatment of the patients was good, with no grade 4 or above treatment-related adverse reactions or death. Conclusions: ETS and DpR may be predictive indicators of the efficacy and prognosis of PD-1 inhibitors combined with trastuzumab and first-line chemotherapy for HER-2 positive advanced gastric cancer.