PD-1 and PD-L1 exhibited somewhat a tendency of positive correlation in scatter plots, the level of expression of these two between the high- and low-risk groups was marginally significant ( p = 0.054 and p = 0.059, respectively).
Because this highly significant PPI enrichment p-value confirmed that the network connectivity was not arbitrary but statistically meaningful, the top 50 genes with the highest degree of connectivity were defined as hub genes (Fig. 2 D) and selected for subsequent prognostic modeling.These 50 hubs were furthered to undergo both univariate and multivariate Cox proportional hazards regressions to filter independent prognostic variables.