While it seems Roche & BMY/MRK started off on opposite sides of the fence regarding PD-L1 expression on immune cells vs. tumor cells, everyone seems to be moving towards a happy medium. Tecentriq lung diagnostic is based on both immune and tumor cells, and Keytruda data in first line bladder from this weekend showed very good ORR in patients selected with combined tumor and immune cell assay.
Given what we know about PD-L1 expression as dynamic and heterogeneous, I'm more inclined to think that the differences in tumor vs. immune cell expression are arbitrary/due to random luck rather than having some underlying biologic or drug-related rationale (probably a little bit of all 3).
News 
Market Data 
Discover 
