Depiction of the combined breast tumor dataset. (A) Table summarizing the different approaches used to obtain the various modules. PCA, principal component analysis. (B) Hierarchical cluster analysis of 323 gene expression modules (rows) across the microarray data of 550 node-negative breast cancer patients (columns). All samples were stratified by source, platform and clinical variables, and randomly split into a training (~2/3) and testing (~1/3) sets.