Supervised analysis of metabolites by estrogen receptor (ER) status. (A) Tumor-specific metabolites were zero-transformed against the mean of the five normal breast tumors, filtered and arranged by hierarchical clustering based on 16 ER + and 9 ER- tumors. (B-D) Significantly higher levels of metabolites in the glycogenolysis (B) and glycolysis (D) pathways, as shown in (C), were found in the ER- compared to ER + tumors. The names of elevated (labeled in red) and reduced (labeled in green) metabolites in the glycolysis (B) and glycogenolysis (D) pathways are shown in the metabolism diagram (C). Increased levels of gamma-glutamyl-isoleucine (E) and reduced (GSH) and oxidized (GSSG) glutathione (F) were also found. Primary data and P values for these comparisons can be found in Table S2 in Additional file 2 and Table S3 in Additional file 3.