Neoadjuvant therapy using PD-1 inhibitor plus chemotherapy with different intervals between chemotherapy cycles for locally advanced gastric or gastroesophageal junction cancer: A randomized phase 2 study.

4064 Background: To explore the influence of reducing dose-intensity of chemotherapeutic agents by prolonging the interval of chemotherapeutic cycles on clinical efficacy, especially when combined with immune checkpoint inhibitors, we conducted a single-center, prospective, randomized, phase II exploratory study in patients with locally advanced gastric or gastroesophageal junction (G/GEJ) cancer. Methods: Patients were randomly assigned to receive either toripalimab plus FLOT regimen for four biweekly cycles or three triweekly cycles before the operation. The primary endpoint was pathological complete response (pCR) rate, the secondary endpoints were major pathological response (MPR) rate, event-free survival (EFS), and safety. Results: 70 patients were enrolled; of these, 69 were eligible for inclusion. The overall pCR rate was 26.1% and the MPR rate was 55.1%. There were no statistical differences in pCR rates and MPR rates between the two groups. Although no statistical differences were found among the subgroups, the pCR rate for patients with PD-L1 CPS ≥1 was 42.1% (8/19) while 6.7% (1/15) for PD-L1 CPS<1 in the triweekly group ( P=0.047). Analysis of lymphocyte subsets in peripheral blood showed that CD3+CD8+PD-1+Ki-67+ T lymphocyte absolute counts were elevated in triweekly group and reduced in biweekly group before the second and third cycle of therapy. The incidence rates of pyrexia and myelosuppression in the biweekly group were higher than those in the triweekly group. Conclusions: These data support the idea that the efficacy of toripalimab plus FLOT, given triweekly for three cycles, was not inferior to its administration biweekly for four cycles in locally advanced G/GEJ cancer. The finding is particularly significant for those with PD-L1 CPS ≥1 and warrants further validation. Clinical trial information: NCT04891016 .