PDCD1 and neoplasm: While most studies concur thata higher level of tumor cell membrane PD-L1 expression is associated with improvedoutcome/response to PD-1/PD-L1 blockade, there is evidence that a subpopulation ofpatients with PD-L1-negative tumors may also have clinical benefit from CPIs.60 The heterogeneity and dynamics of PD-L1 expression confound its use as apredictive biomarker.