CD274 and neoplasm: Tumour cells can express PD-L1 by two general mechanisms: adaptive immune resistance, where PD-L1 expression is upregulated in response to inflammatory factors (such as interferon gamma (IFNγ)) produced by an anti-tumour immune response, and innate immune resistance, where PD-L1 expression is upregulated in response to constitutive oncogenic signalling [9].