ALK and neoplasm: PD-L1 expression on tumor cells can be induced by cytokines secreted by activated T cells (favoring the adaptive immune resistance) or due to constitutive expression induced by genetic alterations (such as EGFR/KRAS mutations, ALK rearrangements, PTEN loss) or activation of signaling pathways (intrinsic immune resistance) [10,19,38,53,77,86,96,200].