CD274 and small cell lung carcinoma: Second, as PD-L1 expression or tumor mutational burden (TMB) was not assessed in the majority of patients, the association between PD-L1 expression or TMB and efficacy of ICIs was not analyzed; however, previous clinical trials have found that the antitumor activity of ICIs in SCLC in the first- or later-line settings is not influenced by PD-L1 expression or TMB value [23, 26, 33].