PDCD1 and cancer: The recent development of immune checkpoint inhibitors (ICIs) for cancers such as melanoma and lung cancer have provided additional options to treat HCC, and anti-programmed cell death protein-1 (PD-1) agents such as nivolumab and pembrolizumab have been approved by the Food and Drug Administration (FDA) as second-line treatments after sorafenib based on phase I/II clinical trial results [1,2] with an approximately 20% objective response rate.