ERBB2 and breast cancer: Since an extensive co-expression of ERBB2 and EPOR has been described in breast cancer [29] and ERBB2 protein levels correlates with that of ERBB2 mRNA [30,31], we evaluated the relationship between ERBB2 and EPOR using gene expression data from 69 breast cancers with low and intermediate levels of ERBB2 (data from proprietary microarray experiments, average or two probes for each gene).