PD-L1 expression on tumor cells is often epigenetic or signaling-driven and cannot be determined by DNA sequence alone.

“that marker is that's not a mutational process in the vast majority of patients it is it's expressed uh from the promoter like you know just turned on for you know reasons having to do with signaling epigenetic reasons etc and so you can't tell by looking at the sequence in dna of pdl-1 whether the tumor is has this marker it's not a mutation marker”