Abstract
11015 Background: In vitro and in vivo data demonstrate that the expression of estrogen receptor (ER) in breast cancer is mainly associated with low proliferation. Gene expression profiling has recently been used to identify a group of high proliferating estrogen receptor positive breast cancers (the luminal B subtype), which are associated with a prognosis that is even worse than that of high proliferating estrogen receptor negative tumors. The analysis of those tumors might provide valuable information about breast cancer biology and could be helpful for adjuvant or neoadjuvant treatment decisions.Methods and Results: We analyzed microarray data from breast cancer specimens to gain insight into genes which play a role in estrogen receptor signalling. Genes were identified showing strong expression in high proliferating ER-positive tumors but no expression in either Ki67-/ER+ or Ki67+/ER- samples. Among these genes the Na+/H+ exchanger regulatory factor NHERF1 was found. We assessed the clinical relevance of NHERF1 transcript levels using a total of 2469 breast cancers. Analysis indicates that enhanced NHERF1 expression is associated with metastatic progression and poor prognosis of breast cancer patients. We found no correlation between NHERF1 and the nodal status as well as age, but positive correlations for tumor size (P<0.001), grade (P<0.001) and erbb2 (P=0.033). Weak NHERF1 expression correlated with longer disease free survival (DFS) in grade 1 and 2 tumors, but not in grade 3 breast cancers. Since NHERF1 expression is strongly linked to the presence of ER, the predictive value for endocrine treatment was analyzed. For samples with weak or none NHERF1 expression a treatment benefit was observed (P=0.007). While untreated patients display a 10 yr DFS rate of 67.2 ± 3.8%, endocrine treatment resulted in 80.1 ± 4.0%. In contrast no differences in disease free survival were found for corresponding NHERF1 expressing breast cancers. Conclusions: Our data indicate that expression of NHERF1 defines a state of differentiation, where breast cancer cells are refractory to endocrine treatment. No significant financial relationships to disclose.
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