Objective To investigate the changes of dendritic cells (DC) in tumor-free,microme-tastasis and tumor-containing lymph nodes from patients with breast cancer.Methods ( 1 ) Micrometastases in 477 pathologically negative lymph nodes from 53 cases of patients with breast cancer were assessed by using immunohistochemistry with cytokeratin-19 antibody.According to the results,the lymph nodes from 53 cases of patients with breast cancer were divided into tumor-free,micrometastasis and tumor-containing lymph nodes; (2) The number of DC in tumor-free,micrometastasis and tumor-containing lymph nodes was assessed by using immunohistochemistry with S-100 antibody,CDla antibody and CD83 antibody respectively.Results Thirty-six of 477 pathologically negative lymph nodes were detected with microme-tastasis.The number of S-100 positive DCs in micro-metastasis and tumor-containing lymph nodes was significantly less than that in tumor-free lymph nodes ( both P ＜0.01 ).There was no significant difference in the number of CDla positive DCs in tumor-free,micrometastasis and tumor-containing lymph nodes (P＞0.05 ).The number of CD83 positive DCs in micro-metastasis lymph nodes was significantly more than that in tumor-free lymph nodes (P ＜ 0.01 ).Conclusion When patients with breast cancer have metastasis in regional lymph nodes,the total number of DC in those lymph nodes would be decreased,resulting in local anti-tumor immunity declined.But at micrometastatic stage of lymph nodes,the number of mature DC is increased relatively with local anti-tumor immunity declined gently.