PDCD1LG2 and head and neck squamous cell carcinoma: PD-L1 and PD-L2 promoter methylation and its mRNA expression were analyzed based on Infinium HumanMethylation450 BeadChip and RNA-Seq (both Illumina, Inc.)data in a representative HNSCC patient cohort (n = 528) enrolled by The Cancer Genome Atlas (TCGA) Research Network.