Comparison of primary breast tumour gene expression profiles generated on Affymetrix and Illumina platforms. The Nadiri et al.  study used Illumina WG6v1 BeadChips, whilst the Desmedt et al. dataset  was generated with Affymetrix HG-U133A arrays. A) Before cross-platform correction. B) After XPN. Hierarchical clustering of tumours is based upon the 500 most variable genes (thumbnails show all genes). i) Subtypes were assigned by three methods Sorlie et al. (2003) , Parker et al. and Hu et al. . Red = basal, purple = ERBB2, blue = luminal A, light blue = luminal B, green = normal-like. Clusters of genes associated with the subtypes are highlighted as follows; ii) ERBB2 gene cluster, iii) luminal gene cluster, iv) basal gene cluster.