MMP9 and ovarian cancer: HIF‐1α binds to AEG‐1 promoter and induces upregulated AEG‐1 expression to enhance metastasis in ovarian cancer by increasing MMP2 and MMP9 expression as well as attenuating E‐cadherin and β‐catenin expression during hypoxia, which is a typical feature of tumor microenvironment.