CD274 and neoplasm: PD-L1 expression and tumor mutational burden (TMB) are both considered independent predictive biomarkers of response to immunotherapy; however, they still lack complete reliability, as objective and durable responses can be observed among patients with low levels of one or both biomarkers, while both primary and acquired resistance are frequent events, even in the presence of high PD-L1 and/or TMB levels [73,74,75].