Significantly higher MMP-1, MMP-2, MMP-3, MMP-7, MMP-9, MMP-10, MMP-11, and MMP-13 levels were found in tumours compared with normal mucosa, and MMP-9 might be useful for evaluating the malignant potential of head and neck squamous cell carcinoma [14]. Here, MMP9 is linked to head and neck squamous cell carcinoma.