<p>Th7R is a novel Th1-like CD4⁺ T cell lineage characterized by TCF7 and IL-7 receptor expression, exhibiting distinct transcriptional and epigenetic profiles compared with classical Th1 cells. The clinical significance of Th7R, including the efficacy of immune checkpoint inhibitors and the prediction of postoperative disease-free survival, has been demonstrated in non–small cell lung cancer (NSCLC) but not in small cell lung cancer (SCLC). In this study, we investigated Th7R expression as a predictive marker in patients with extensive-stage SCLC (ES-SCLC) who received chemotherapy or chemo-immunotherapy (n = 47). Results showed that Th7R was positively correlated with progression-free survival (PFS) after treatment and that long-term PFS was observed only in patients with Th7R^high who were treated with anti-programmed cell death-1 ligand 1 (PD-L1) antibody combination therapy. Furthermore, high Th7R levels were associated with significantly better overall survival. Th7R showed a positive correlation with GZMB⁻GZMK⁺ precursor exhausted CD8⁺ T cells (Tpex), which are known target cells for PD-1 blockade therapy. These findings suggest the presence of the Th7R–Tpex axis. Th7R, which reflects antitumor T-cell immunity, is a useful predictive marker for treatment efficacy in ES-SCLC.</p>