Efficacy of immunotherapy in advanced gastric cancer: preliminary results of a multicenter observational study

Background: Due to the low efficacy of PD-L1 antibodies in second and subsequent lines of metastatic gastric cancer (mGC), the optimal treatment strategy of such patients and appropriate choice of predictive biomarkers remain challenging. The aim of our study is to assess the efficacy of immune checkpoint inhibitors monotherapy in patients with mGC in routine clinical practice, especially in heavily-pretreated patients. Materials and methods: We retrospectively analyzed data of patients treated in five oncology centers in Moscow between 2018 and 2023, who received nivolumab or pembrolizumab for advanced gastric cancer. Primary end-point of our study was 6-months PFS. Secondary end-points were overall survival (OS), objective respons e rate (ORR), and disease control rate (DCR). Toxicity was assessed using CTC AE v5.0 scale. Results: 122 patients with mGC who received immune checkpoint inhibitors were included between 1 January 2018 and 28 February 2023. 6-months PFS rate was 31,6 %. The median OS was 7 months (95 % CI: 2–20), the median PFS was 3 months (95 % CI: 1,5–9,5). A statistically significant difference in OS was detected in patients with MSI compared to MSS (25 months vs 6 months; 95 % CI: 0,21–0,86; HR: 0,43). A trend towards higher PFS was observed as well (10 months in MSI vs 3 months in MSS; 95 % CI:0,26–1,01; HR: 0,51). No statistical significance in PFS and OS according to PD-L1 CPS was found among patients with MSS. ORR and DCR were 36,6 % and 10,6 %, respectively. No cases of pseudoprogression or fatal immune-related AEs were observed. Conclusion: Our real-world data is consistent with published literature and the results from clinical trials. Further studies are needed to determine prognostic factors and to establish prognostic model of patients receiving ICIs for optimal treatment strategy of mGC.