By establishing an orthotopic mouse model of MDA-MB-231 cells, previous studies have explored a novel transforming growth factor-beta1 (TGF-β1)/cyclin-dependent kinase 5 (CDK5)/HOTAIR/H3K27 signaling that could promote tumor growth, lymph node metastasis, and breast-to-lung metastasis [69]. The gene discussed is CDK5; the disease is neoplasm.