While fatigue is reported by almost 90% of obese patients with MPNs [39], the lack of comparative data from non-obese MPN cohorts limits our ability to determine whether this high prevalence is primarily attributable to the underlying neoplasm, obesity-related factors, or their interaction; the cytokine most responsible for fatigue would be TNFα, which, in fact, is increased both in patients with MPN and in the general obese population [40,41]. Here, TNF is linked to obesity due to melanocortin 4 receptor deficiency.