PVR and hepatocellular carcinoma: Qin et al., (2011) demonstrated that GPR18 was overexpressed in melanoma metastases and may be highly relevant for the malignant behaviour of melanoma. However, in our study, GPR18 was identified as a protective factor for HCC patients. PVRIG (PVR related immunoglobulin domain containing), also known as CD112R, is a member of the poliovirus receptor–like proteins, preferentially expressed on T cells and NK cells (Zhu et al., 2016). Blockade of CD112R enhanced trastuzumab-triggered antitumour response by human NK cells and could be used to treat breast cancer (Xu et al., 2017).