Table 2. Potential Explanations for Discrepencies between Clinical Response to PD-1-PD-L1 Blocking Therapies and Intratumoral PDL1 Expression.

	Clinical Response
PD-L1 expression	Non responding	Responding
PD-L1 negative		false negative in assays role of PD-L1 outside of the tumor microenvironment dynamic nature of PD-L1 expression role of PD-L2
PD-L1 positive	other suppressive mechanism(s) tumor insensitivity to T cells expression of PD-L1 not due to an ongoing immune response