MMP9 can also activate several latent proteinases and angiogenic factors or cytokine receptors, which enhance invasion and metastasis.39 MMP9 is a cancer promoter in PTC, for example, MMP9 is up‐regulated and correlates with tumour diameter, lymph node metastasis, degree of PTC infiltration and clinical stage.40, 41 We found that si‐KDM1A reduced MMP9 expression and activation, suggesting that it may promote tumour progression by regulating MMP9. The gene discussed is KDM1A; the disease is cancer.