HOTAIR facilitated tumorigenesis and tumor development by regulating multiple molecules (e.g., vascular endothelial growth factor (VEGF) and E-cadherin and matrix metalloproteinase-9 (MMP-9)) that were connected with epithelial-to-mesenchymal transition (EMT), tumor invasion, and metastasis. The gene discussed is MMP9; the disease is neoplasm.