IGFBP3 and obesity due to melanocortin 4 receptor deficiency: Obesity is hypothesized to promote tumor progression by (1) producing higher concentrations of estrogen and testosterone [2, 17, 18], (2) contributing to insulin resistance, leading to increased levels of insulin-like growth factor-I (IGF-1) and insulin-like growth factor-binding protein-3 (IGFBP-3) [10, 19, 20], and (3) contributing to chronic inflammation [21].