Interpretation of PD-L1 expression
The slides were reviewed and scored independently by two clinical pathologists specialized in in interpreting PD-L1 expression in solid tumors. PD-L1 was scored according to the quantity and intensity in the megakaryocytic lineage of cells. The quantity of PD-L1 expression was graded from 0 to 100% while the intensity was graded from 1+ to 3+, according to the level of intensity. The result was a PD-L1 score calculated by multiplying percentage by intensity of PD-L1 in the bone marrow megakaryocytes. This score will be detailed further in the statistical analysis section.