Increasing numbers of reports have provided evidence that aberrant DNA methylation, especially that by DNA methyltransferases, has a critical role in the different subtypes of thymoma.27 DNMT1, together with DNMT3A, DNMT3B, and DNMT3L cooperating with each other, are a group of catalytically inactive DNA methyltransferases.28 Compared with the KITLGhigh and KITLGlow groups, using TCGA‐THYM data, DNMT3B showed significantly higher expression in the KITLGhigh group (P < 0.0001). This evidence concerns the gene DNMT3L and thymoma.