POLD1 and head and neck squamous cell carcinoma: Likewise, POLD1 expression was significantly positively correlated with MSI in ACC, BLCA, BRCA, CESC, head and neck squamous cell carcinoma (HNSC), KICH, KIRC, HCC, LUAD, LUSC, PRAD, SARC, STAD, THCA, and UCEC (Supplementary Figure S3D).