FGFR1 and obesity due to melanocortin 4 receptor deficiency: The notable rise in FGF21 that is specific for adipocyte FGFR1-KLB and correlates with the delay in breast tumor progression suggests that FGF21 and its agonists may be of similar benefit for control of breast tumor progression, as they are for alleviation of obesity and diabetes via the adipocyte compartment.