Copper‐transporting P‐Type Adenosine Triphosphatase (ATP7B) Is Expressed in Human Breast Carcinoma

This is the first report to show that a copper‐transporting P‐type adenosine triphosphatase, ATP7B, is expressed in certain breast carcinomas, and a priori knowledge of its expression is important for the choice of therapy. We investigated the hypothesis that ATP7B, which was shown to be associated with cisplatin resistance in vitro, is expressed in certain breast carcinomas. To test this hypothesis, ATP7B expression and protein level were examined in 41 breast carcinomas using RT‐PCR and immunohistochemistry. ATP7B gene/protein could be detected in 22.0% (9/41) of breast carcinomas and ATP7B gene expression was correlated well with the protein expression. In nine ATP7B‐positive tumors, adjacent normal breast tissue was similarly analyzed, revealing that ATP7B is upregulated in breast carcinoma. ATP7B gene expression in poorly differentiated carcinoma was significantly higher than that in well‐/moderately differentiated carcinoma (P=0.012). Furthermore, we found no association between the ATP7B gene/protein expression and that of MDR1, MRP1, LRP and BCRP. These findings suggested that ATP7B gene expression might be a chemoresistance marker for cisplatin in patients with poorly differentiated breast carcinoma.