HER-2 is an important prognostic factor in breast cancer, and its overexpression is observed in 20-60% of cases with micrometastases in the bone marrow. The aim of this study was to explore the potential functional role of HER-2 in primary breast tumors with bone metastases. Forty-eight primary breast tumors with simultaneous or non-simultaneous bone metastases were studied. The expression of hormone receptors, and metastasis and growth factor-related proteins were assessed by immunohistochemical staining. The correlation in statistical significance was assessed by the Chi-square test. Of the 48 breast tumors, 11 (22.9%) were HER-2-positive and 37 were HER-2-negative. There was no significant difference in HER-2 status and clinicopathologic factors between the two groups. Of the 11 HER-2-positive tumors, there were 2 and 3 cases that showed positive nuclear expression for estrogen and progesterone receptors, respectively. No extranuclear expression of HRs was detected in these tumors. For metastasis-related proteins such as c-Met, VEGF, and MTA-1, which are activated by HER-2, only some insignificant focal expression of these proteins was observed. An increased level of pAkt was observed in 9 (81.8%) of 11 tumors, and an increased expression of CXCR4 was observed in 6 (54.5%) of 11 tumors. The frequency of increased levels of pAkt and CXCR4 was not significant between HER-2-positive and -negative tumors. The increased levels of pAkt and CXCR4 are induced by factors that are both dependent and independent of HER-2, and the activation of HER-2/CXCR4/ Akt signaling pathway in primary breast tumors may contribute to the formation of bone metastases in breast cancer.

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