While the precise transcriptional regulation of OXPHOS-related genes in breast cancers remains to be elucidated in clinical breast cancer tissues, it will be useful to review the clinical relevance of OXPHOS-related transcriptional factors in breast cancers, particularly that of the estrogen-related receptor (ERR) family nuclear receptors and collaborating coactivators peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1). The gene discussed is PPARGC1B; the disease is breast cancer.