CD274 and cancer: From a clinical perspective, there are, therefore, many issues to take into account: the intrinsic variability in PD-L1 expression in cancer population, the potential bias due to aging of the specimens—hence, the practice in some institutions to test patients for PD-L1 at first presentation, irrespective of expected outcome or clinical request, which, however, raises important questions on economic resource use—and, finally, the potential effect of already administered therapy on PD-L1 expression and, thus, eligibility for immunotherapy.