PDIA4 and cancer: The P4HB (also known as PDIA1) and PDIA4, which were chosen from the six-gene signature, belong to the protein PDI protein family and have been proved to be related to ER stress activation in human cancers (Joo et al., 2007; Kranz et al., 2017; Winship et al., 2017; Liu et al., 2019; Wang et al., 2020), especially the PERK signaling pathway (Kranz et al., 2017, 2020).