Abstract
Basal breast cancers (BBCs) have a high risk of metastasis, recurrence and death. Formal subtype definition relies on gene expression but can be approximated by protein expression. New markers are needed to help in the management of the basal subtype of breast cancer. In a previous transcriptional analysis of breast cell lines we found that Moesin expression was a potential basal marker. We show here that Moesin protein expression is a basal marker in breast tumors. In a tissue microarray (TMA) containing 547 sporadic breast cancers, of which 108 were profiled for gene expression, Moesin was expressed in 31% of all tumors and in 82% of the basal tumors. To confirm that Moesin expression remained associated with the basal phenotype in specific types of BBCs, we analyzed Moesin expression in 2 other TMAs containing 40 medullary breast cancers (MBCs) and 27 BRCA1‐associated breast cancers (BRCA1‐BCs), respectively. Moesin was strongly expressed in MBCs (87%; p = 2.4 × 10^−5^) and in BRCA1‐BCs (58%; p = 1.3 × 10^−5^) as compared with non‐MBCs and sporadic cases. Moesin‐expressing tumors display features of BBCs, such as high proliferation rate, hormone receptors negativity, expression of putative basal/myoepithelial markers (CAV1, CD10, CK5/6, CK14, EGFR, P53, P‐cadherin and SMA). Survival analysis showed a reduced specific survival and metastasis‐free survival in Moesin‐expressing tumors by log‐rank test (p~SS~ = 0.014 and p~MFS~ = 0.014). In multivariate analysis, Moesin expression was nearly an independent prognostic marker of poor outcome as shown by Cox proportional hazard model in patients without lymph node metastasis (p = 0.052, HR = 2.38, CI 95[0.99–5.69]). © 2007 Wiley‐Liss, Inc.