Breast Cancer Research Vol 9 No 6 Rakha et al. remarkably low prevalence of EGFR expression in TNP tumours, the results of Kreike and colleagues [1] are in agreement with those of several previously published comparisons on the IHC features of basal-like tumours as defined by expression arrays, which clearly demonstrate that most, but certainly not all, have a TNP phenotype [8, 11, 12]. In fact, ER IHC expression and HER2 3+ or gene amplification are reported to be found in 5% to 45% and 5% to 15% of basal-like tumours as defined by expression arrays, respectively [3, 8, 9, 11, 12]. In addition, Harris and colleagues [13] recently reported on a subgroup of HER2-amplified breast cancers that harbour a basal-like transcriptomic profile.

Previous studies have shown that the expression of ‘basal markers’(that is, Ck 5/6, Ck 14, Ck 17, and/or EGFR) is associated with a poor prognosis [5-7, 14], regardless of hormone receptor expression. The expression of basal markers (basal cytokeratins and EGFR) in TNP tumours (core basal phenotype) also correlates with a worse prognosis and identifies a clinically distinct subgroup within the TNP group [5, 7]. Moreover, it should be noted that identification of a subgroup of tumours solely based on the lack of expression of immunohistochemistry (for example, TNP) risks misassignment based on technical artifacts [3, 4].