Hierarchical clustering with bootstrapping of adjacent and reduction breast tissues from gene expression data. (a) Hierarchical clustering with bootstrapping of adjacent and reduction epithelium. (b) Histologically normal adjacent and reduction stroma. (c) Histologically normal adjacent epithelium. (d) Histologically normal adjacent stroma. We used 10,000 bootstrap iterations to obtain significance scores for the observed clusters. Nodes are labeled with the percentage of times that the cluster is observed by bootstrapping. Only adjacent stroma showed statistically significant clusters at the top level. Red boxes indicate the top-level clusters that were tested for association with clinical characteristics of the samples.