Breast cancer subgroups defined by estrogen receptor message (ESR1) expression, ERRB2 amplification and BRCA1/BRCA2 mutation status. (a) ESR1 values in the van't Veer and colleagues tumor samples . The expression ratios for ESR1, ERRB2 and GRB7 along with the mutational status of BRCA1/BRCA2 were used to delineate the breast cancers into six subgroups. The ERBB2-positive tumors (purple) are grouped separately and arranged from highest to lowest ESR1 level. The samples containing BRCA1 or BRCA2 mutations (dark green) are also grouped separately and arranged from highest to lowest ESR1. The two BRCA2 samples are marked with asterisks. The remaining tumors are arranged by ESR1 level and colored as highly positive (black; ESR log ratio > 0.2), moderately positive (blue; ESR1 > 0 and ESR1 < 0.2), weakly positive (yellow; ESR1 < 0 and ESR1 > -0.5), and negative (red; ESR1 < -0.5). The dotted line represents an estimation of true estrogen receptor (ER) negativity by immunohistochemistry comparison. (b) High ERBB2 expression levels are the result of gene amplification. The samples are arranged in the same order and colored as in (a). Upper, ERRB2 intensity ratios; lower, co-amplified GRB7 intensity ratios.