Effect of induction immunochemotherapy before concurrent chemoradiotherapy on outcomes in limited-stage small cell lung cancer.

e20158 Background: Immunotherapy, chemotherapy, and radiotherapy all play significant roles in the management of small cell lung cancer (SCLC). Combining radiotherapy with chemotherapy followed by immunotherapy shows promise for limited-stage SCLC (LS-SCLC), offering good tolerability and survival benefits. However, there is limited data on whether immunotherapy combined with chemotherapy for LS-SCLC can be performed before chemoradiotherapy. Therefore, we investigated the safety and effectiveness of induction immunochemotherapy followed by concurrent chemoradiotherapy (CCRT) for LS-SCLC. Methods: A retrospective analysis was conducted on 138 patients with LS-SCLC who received chemoradiotherapy between January 2019 and December 2024. This study included 34 patients receiving induction immunochemotherapy and 104 patients receiving induction chemotherapy. All patients underwent 2-4 cycles of induction therapy before CCRT. Clinical outcomes, including survival and toxicity, were compared between groups. Imaging assessments were performed before and 1 month after CCRT. The evaluations included the tumor response to induction therapy, treatment-related adverse events, complications during and after CCRT, tumor response after CCRT, progression-free survival (PFS), and overall survival (OS). Follow-up data were collected through regular check-ups or inpatient records. Results: Compared to the induction chemotherapy group, the objective response rate (ORR) of tumors after induction treatment in the induction immunochemotherapy group was 67.6% (23/34) versus 45.2% (47/104) (P = 0.023). After CCRT, the ORR in two groups was 79.4% (27/34) versus 60.6% (63/104) (P = 0.045). The median follow-up time was 25.3 months for the induction immunochemotherapy group and 28.2 months for the induction chemotherapy group. The median progression-free survival (PFS) for two groups was 21.3 months versus 13.1 months (P = 0.015), and the median overall survival (OS) was not reached versus 41.7 months (P = 0.039). Treatment-related toxicities of grade 1-2 were 64.7% versus 54.8% (P = 0.311), and grade 3-4 toxicities were 41.2% versus 41.3% (P = 0.986). No grade 5 treatment-related toxicities were observed. Conclusions: Induction immunochemotherapy followed by CCRT for patients with LS-SCLC is effective and safe with a high ORR, PFS and OS rate, as well as a tolerable toxicity profile. Larger, randomized controlled trials are required to confirm our findings. Characteristics Induction immunochemotherapy (n=34) Induction chemotherapy (n=104) Best response to induction therapy-n(%) CR/PR 23 (67.6) 47 (45.2) SD 10 (29.4) 52 (51.0) PD 1 (2.9) 4 (3.8) Best response to CCRT-n(%) CR/PR 27 (79.4) 63 (60.6) SD 6 (17.6) 34 (32.7) PD 1 (2.9) 7 (6.7) The median progression-free survival-months 21.3 13.1 The median overall survival-months NR 41.7