Kishibuchi et al. [48] found that promoter methylation of HOXD9 was significantly higher in thymic carcinoma than in thymoma and the thymus, and relapse‐free survival was significantly worse in tumors with a higher DNA methylation of HOXD9 in all of the thymic epithelial tumors. Here, HOXD9 is linked to thymic epithelial neoplasm.