PDCD1 and hepatocellular carcinoma: In this regard, Sia et al. have recently proposed a novel HCC classification based upon the tumor immune status: according to this classification, about 30% of HCCs could be categorized into an ‘immune class’, with high levels of immune cell infiltration, expression of PD-1 and/or PD-L1, activation of interferon-γ signaling, and markers of cytolytic activity [30].