IFNG and cancer: There are three patterns of PD-L1 expression in cancer: (a) cancers that constitutively express PD-L1 due to genetic alterations including amplification of the PD-L1 locus; (b) cancers that express PD-L1 induced by IFNγ, which is secreted by tumour-infiltrating T cells, in a process known as “adaptive immune resistance”; and c) cancers that do not express PD-L1, including those with a genetic event that prevents PD-L1 expression (Ribas and Hu-Lieskovan, 2016).