Cell-type-specific cytokeratin expression in breast cancer subgroups. The log ratios for the cytokeratin probes for the van't Veer and colleagues tumor samples  are colored by group as in Fig. 3. (a) Co-expression of the luminal KRT8 and KRT18 is found in the estrogen receptor (ER)-positive tumors (black, blue and yellow) and in the ERRB2-positive tumors (purple). (b) Co-expression of the basal KRT5 and KRT14 is found in the ER-negative tumors (red) and in the BRCA1 mutant tumors (dark green).