Additionally, a Cox regression analysis revealed no significant correlation between different clinical parameters—such as age, metastatic site, and smoking status—and patients’ survival (Table S4) More importantly, patients with PD-L1+CTCs isolated from treatment-naïve ES-SCLC and high levels of PD-1+-expressing CD3+CD8+ T-cells have a survival advantage when treated with the standard chemotherapeutic regimens together with ICI in a front-line setting. Here, CD274 is linked to small cell lung carcinoma.