Hierarchical clustering using 'intrinsic' genes. (a) Five groups were identified, namely the highly proliferating luminal (light blue), luminal A (dark blue), normal-like (green), basal-like (red) and ERBB2+ (magenta) groups, which were used in the survival analysis. (b) Hierarchical clustering was performed using 540 clones, representing 496 unique genes from the 'intrinsic' gene list. The individual color of the dendrogram branches reflects the correlation with centroids previously described, and tumors with low correlation (<0.2) with a specific subtype are here indicated by gray branches. Gene clusters characterizing the five groups (a) involve genes encoding, for example, (c) estrogen receptor (ER), (d) MUC1, (e) cadherin 1 (E-cadherin; CDH1), (f) FOXC1 and (g) ERBB2. Since very few genes associated with cell division and proliferation are part of the 'intrinsic' gene list, such a cluster was selected from the total list of genes (Additional file 4), clustered and organized according to (h) the 'intrinsic' dendrogram to show the difference in proliferation between the two luminal groups. (i) In the same manner, a gene cluster characteristic of the mucinous breast carcinomas was made from the total list of genes.