ALK and non-small cell lung carcinoma: Different from classical “binary” (positive or negative) biomarkers in NSCLC, such as EGFR activating mutations and ALK rearrangements, the expression of PD-L1 is a continuous variable, starting from zero through to high levels, and the use of thresholds to define if the IHC assay is positive or negative is artificial, generating the illusion of a binary system.