Effect of reducing the number of neoadjuvant chemoimmunotherapy cycles on clinical efficacy in locally advanced PD-L1 positive gastric cancer: A single center phase 2 study

e16074 Background: The standard therapeutic recommendation is neoadjuvant chemotherapy with FLOT regimen following radical resection in patients with locally advanced gastric cancer. It is not clear whether neoadjuvant anti-PD-1 antibody plus FLOT regimen could improve the pathological complete response (pCR) rate and how to combine anti-PD-1 antibody and FLOT regimen. We conduct this phase II study to explore this problem (NCT 04891016). Methods: This study is a prospective clinical study, patients are randomly enrolled into the experiment group and the control group according to the random number method. The patients in the experiment group receive standard dose of FLOT regimen plus toripalimab every three weeks, toripalimab is administered on third day in each cycle, after three cycles operation is performed. The patients in the control group receive standard dose of FLOT regimen plus toripalimab every two weeks, toripalimab is administered on the first day in each cycle, after four cycles operation is performed. The primary endpoint is pCR and the secondary endpoint is recurrence-free survival. Results: From June 2021 until present, 57 patients with locally advanced gastric cancer were enrolled in this study, including 28 patients in the experiment group and 29 in the control group. Three patients in the experiment group and two in the control group withdrew from the study as to the influence of COVID-19’s epidemic or personal reason. One patient in the experiment group postponed operation due to immune-related thrombocytopenia. The remaining 51 patients completed the prescribed chemotherapy plus toripalimab and operation, and all the operations were R0 resection. Among these 51 patients, pCR was got in 16 patients and the pCR rate was 31.4%, MPR rate was 66.7%. Further analysis according to the expression of PD-L1 is shown. The overall incidence of adverse events was 93%. The incidence and severity of myelosuppression in the experiment group were lower than those in the control group. Among all the patients received R0 resection, 6 patients experienced recurrence and the remaining are still kept in recurrence-free status. The recurrence-free survival is not available at present. Conclusions: 1) Neoadjuvant therapy with FLOT plus toripalimab is safe and effective in locally advanced gastric cancer. 2) Postponing the use of toripalimab when combined with FLOT as neoadjuvant regimen in locally advanced gastric cancer patients with PD-L1 CPS ≥1 could reduce the number of chemotherapy cycles and thus reduce the adverse events of chemotherapeutic drugs, while the dose intensity of chemotherapy is import in patients with PD-L1 CPS ＜1. Clinical trial information: NCT04891016 .[Table: see text]