In addition, it is interesting to speculate that the upregulated oxidative metabolism and detoxification enzyme expression observed in obesity (a variable linked to high blood cholesterol levels), as detected in the basal-like breast tumours of overweight/obese versus lean breast cancer patients, is possibly mediated via the cholesterol–ERRα axis, and that this upregulation increases cell proliferation and may cause resistance to chemotherapeutics and some targeted therapies [15,16,17,69]. This evidence concerns the gene ESRRA and obesity due to melanocortin 4 receptor deficiency.