Among the exploratory objectives of this study, there are to be determined whether baseline TMB is predictive for response to therapy in SCLC patients, whether changes in blood-based TMB during treatment may predict clinical benefit in the whole population, and whether a composite immune- and tumor-cell-staining score can be developed, with or without PD-L1 by immunohistochemistry, to predict response in the SCLC cohort. The gene discussed is CD274; the disease is neoplasm.