Pearson correlation analysis demonstrated that the serum MMP-9 concentration was positively correlated with malignancy (P<0.001), tumor size (P=0.029), lateral lymph node metastasis (P<0.001), extrathyroidal invasion (P=0.022), presence of distant metastasis (P=0.022), and TNM stage (III+IV) (P<0.001), as shown in Table 2. This evidence concerns the gene MMP9 and metastatic malignant neoplasm in the lymph nodes.