CD274 and small cell lung carcinoma: However, the overall expression of PD-L1 in SCLC was relatively low in most studies compared with NSCLC.133 In addition, the lack of correlation between efficacy and PD-L1 expression in this trial is not only consistent with the results of an earlier phase I clinical trial of atezolizumab monotherapy in patients with relapsed or refractory SCLC134 but also the other completed studies of ICIs in patients with untreated ES-SCLC.135 Therefore, the use of atezolizumab in patients with ES-SCLC does not mandate PD-L1 testing and expression.136,137