In extensive-stage small-cell lung cancer (ES-SCLC), IMpower133 improved progression-free survival (PFS) and overall survival (OS) of the etoposide/carboplatin plus atezolizumab (ECT) combination, but the absolute benefit was modest. For a study, researchers sought to determine if the expressive status of Yes-associated Protein 1 (YAP-1) might be used to screen most ES-SCLC patients for immunotherapy. They enrolled 21 patients with ES-SCLC who got an ECT treatment and whose formaldehyde-fixed, paraffin-embedded material was attainable from January 2018 to July 2021 at the institution. The effectiveness assessment criteria of solid tumor (RECIST) version 1.1 were used to determine complete remission (CR), partial remission (PR), disease stable (SD), and progressing disease (PD). YAP-1 (ET1608-30, 1/100) was studied using immunohistochemistry (IHC). IHC Profiler was used to calculate the H-score. SPSS 22.0, X-tile 3.6.1, and Excel evaluated all statistical analyses. Statistical significance was defined as a P<0.05. The following table contains the baseline data. Responders (CR/PR patients) had a median H-score of 13.97 (95% CI: 8.97-16.30), and non-responders had a median H-score of 23.72 (95% CI: 8.13-75.40), which were substantially different (P<0.05). According to spearman (r=-0.603), the H-score and PFS had a negative connection. According to the H-score cut-off value, patients were classified into two groups: low expression (H-score 25.00, n=16) and high expression (H-score >25.00, n=5). The median PFS for these two groups was 7.1 million (95% CI: 2.6-11.6 million) and 3.4 million (95% CI: 0.9-5.9 million), respectively. However, PFS’s K-M curves differed considerably (P<0.05). The first outcomes suggested that the YAP-1 protein might have significant predictive value. YAP-1 protein expression was also inversely linked with ECT efficacy in ES-SCLC patients