ABSTRACT
The purpose of this study was to classify breast carcinomas based on variations in gene expression patterns derived from DNA microarrays, and to correlate tumour characteristics to clinical outcomes. A total of 85 DNA microarray experiments representing 78 cancers, three fibroadenomas and four samples of normal breast tissue were analysed by grouping tumours together based on their genetic similarity when looking at a large number (thousands) of genes (hierarchical clustering) and their clinical outcomes. Genes were analysed according to whether they were overexpressed or underexpressed, which was then correlated with survival. The cancers could be classified into a basal epithelial-like group, an ERBB2-overexpressing group and a normal breast–like group based on variations in gene expression, and two separate luminal types could be distinguished. Survival analyses on a subgroup of patients with locally advanced breast cancer uniformly treated in a prospective study showed significantly different outcomes for the patients belonging to the various groups, including a poor prognosis for the basal-like subtype and a significant difference in outcomes for the two oestrogen receptor–positive groups.
