Small cell lung cancer (SCLC) is a neuroendocrine tumor with characteristics such as aggressiveness, early metastasis, rapid multiplication time, and easy drug resistance, and generally has a poor prognosis (Das et al., 2021). Although patients with SCLC have a high rate of initial treatment sensitivity, relapse is prevalent and frequently accompanied by chemotherapy resistance, which affects the choice of follow-up therapy (Gong and Salgia, 2018, Karacz et al., 2020). Currently, systemic therapy is advised for patients with relapse, and the suggested medications include paclitaxel, lurbinectedin, topotecan, and immune checkpoint inhibitors (ICIs) (Ganti et al., 2021).

ICIs are popular in clinical treatment due to their excellent efficacy against many tumors and long maintenance times after tumor regression. Moreover, the high tumor mutational load (TMB) and the presence of p53 and RB1 deletion in SCLC have predicted the potential benefit of checkpoint inhibitors in treatment (Roper et al., 2021). ICI has thus been considered by researchers as a potential treatment for recurrent SCLC. Although clinical investigations are ongoing, checkpoint inhibitors have demonstrated tentative efficacy and safety in several clinical trials for recurrent SCLC (Belluomini et al., 2022). However, evidence for ICI in the backline treatment of SCLC is insufficient, and the impact of combination therapy and drug selection on treatment is unclear. To better guide clinical practice, we conducted this single-arm meta-analysis to evaluate the efficacy and safety of ICIs in the backline treatment of SCLC.