The multivariate Cox regression analysis indicated that serum DKK-1 level (HR = 2.19; P = 0.002), TNM stage (HR = 4.24; P = 0.01), and lymph node metastasis (HR = 3.12; P = 0.007) were independent prognostic factors for OS, while serum DKK-1 level (HR = 3.97; P < 0.001), tumor grade (HR = 2.98; P = 0.009), and expression of HER2 (HR = 2.29; P = 0.02) were independent prognostic factors for RFS (shown in Table 2). Here, DKK1 is linked to metastatic malignant neoplasm in the lymph nodes.