In this regard, tumor mutational burden (TMB) and PD-L1 expression are proposed as predictive markers of response to immune checkpoint inhibitors (ICIs) in human tumors, including small-cell lung cancer [45,46], although other recent studies have not reported the association of these biomarker with clinical benefit in extensive small-cell lung cancer treated with ICIs [47,48]. Here, CD274 is linked to small cell lung carcinoma.