Interestingly, patients with stage 2, stage 3 and the most severe stage 4 BC are characterized by a high expression of IDO1 (Fig. 2E) as well as patients with extreme weight (BMI 24.9–29.9) and obesity (BMI 30–34.9) (Fig. 2F), which have been associated with less favorable outcome in BC patients [15]. This evidence concerns the gene IDO1 and obesity due to melanocortin 4 receptor deficiency.