Delayed addition of PD-1/PD-L1 inhibitors into chemotherapy on the outcomes for patients with extensive-stage small cell lung cancer: A propensity score-matched study.

208 Background: Immunotherapy in combination with chemotherapy has become the first-line treatment for extensive-stage small cell lung cancer (ES-SCLC). However, some patients failed to undergo simultaneous immunotherapy at the time of initial chemotherapy, and whether this will have an impact on the efficacy of immunochemotherapy has not been fully explored. Methods: Between January 2020 and December 2022, the study included 416 patients diagnosed with ES-SCLC and receiving first-line immunotherapy, divided into two groups: delayed-IO (administering PD-1/PD-L1 inhibitors at 2-4 Cycles of chemotherapy) and early-IO (administering PD-1/PD-L1 inhibitors concurrent with first-cycle chemotherapy). Propensity score matching (PSM, 1:1) was performed to balance the baseline characteristics of the two groups. The primary endpoints were OS and PFS. Calculations were performed using the Kaplan-Meier method and comparisons were made using the log-rank test. Results: Mainly due to the fact that PD-L1/PD-1 inhibitors were not included in the medical insurance, which was difficult for patients to afford and the poor physical condition of some patients, taking into account the safety of the patients themselves, 72 patients in the delayed-IO group (2 cycles of chemotherapy: 41; 3 cycles: 16; 4 cycles: 15), and 344patients were included in the early-IO group. The median OS and PFS were 24.00 months and 8.75 months in the delayed-IO group, and those were 18.59 months and 7.57 months in the early-IO group, respectively, before PSM. There was no significant difference in OS and PFS between the two groups (HR 0.72; P = 0.054 and HR 0.86; P = 0.281, respectively). After PSM, there were 72 patients in each of the two groups. The median OS in the delayed-IO group and the early-IO group was 24.00 months and 18.79 months, respectively (HR 0.60, 95% CI 0.38-0.97; P = 0.037). Median PFS was 8.75 and 6.49 months in the two groups, respectively (HR 0.69, 95% CI 0.48-0.99; P = 0.044). There was a statistically significant difference between the two groups. The overall adverse event profile was comparable between the two groups. Conclusions: Our findings suggest that administering PD-1/PD-L1 inhibitors at 2-4 Cycles of chemotherapy was superior to administering PD-1/PD-L1 inhibitors concurrent with first-cycle chemotherapy in patients with ES-SCLC, while the safety profile of both was similar.