OBJECTIVE To clarify the expression of MTDH in invasive micropapillary carcinoma of the breast (IMPC) and analyze the relationship between MTDH expression and clinicalpathologic parameters of the IMPC patietns. METHODS The expression of MTDH protein was analyzed using immunohistochemical staining in 86 cases with IMPC and another 86 cases with invasive ductal carcinoma not otherwise specified (IDC-NOS). The association between MTDH expression and clinicalpathologic parameters of the IMPC patients was analyzed. RESULTS Immunohistochemical analysis revealed the high expression of MTDH in 64 of the 86 (64/86, 74.4%) IMPC patients and in 45 of the 86 (45/86, 52.3%) IDC-NOS patients. Statistical analysis showed a statistically significant difference in MTDH expression between IMPC and IDC-NOS (P , 0.05). In IMPC, the expression of MTDH was correlated with lymph nodes metastasis (P , 0.05). The expression of MTDH was negative in normal breast tissue of IMPC and IDC-NOS patients. CONCLUSION High expression of MTDH is one of the molecular mechanisms, which facilitates lymph node metastasis of IMPC, therefore, the expression level of IMPC plays an important role in lymph node metastasis of IMPC.KEY WORDS: breast carcinoma, invasive micropapillary carcinoma, metadherin, lymph node metastases.

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