Nagel et al. found that a disturbed balance exist between MMP and tissue inhibitor of metalloproteinase (TIMP) in malignant salivary gland tumors and suggested that MMP2 expression could be related to the invasive behavior and the malignant potential of these tumors.[7] De Vicente et al. proposed that the high expression of MMP9 could contribute to the prognosis and clinical behavior of malignant salivary gland tumors.[8]. The gene discussed is MMP9; the disease is tumor of salivary gland.