As shown in Table 1 the expression of claudin-6 was not correlated with age (P = 1.000), tumor size (P = 0.444), clinical stage (P = 0.760) or differentiation (P = 0.142) and was inversely correlated with lymph node metastasis of the breast invasive ductal carcinomas (P = 0.021). The gene discussed is CLDN6; the disease is metastatic malignant neoplasm in the lymph nodes.