Mitochondrial differences in breast cancer subtypes were more evident in a PCA analysis (Figure 1B) where a cluster of luminal A and B tumors was found to the left of the graph, followed by an intermediate group with HER2-enriched and luminal B samples and a well-defined Basal-like enriched cluster to the right of the graph which also included some HER2-enriched samples. This evidence concerns the gene ERBB2 and breast cancer.