JAK2 and obesity due to melanocortin 4 receptor deficiency: HFD vs. low fat diet (LFD):- Stimulation of thyroid tumor growth - Increase in Ki-67 positive cells and protein abundance of p-Rb and cyclin D1- No difference in activation of MAPK and PI3K signaling pathways- Promotion of anaplastic change in thyroid cancers - Increased expression of Mcl1, Bcl2l1, Ccnd1, and Vegfa (STAT3 target genes) and activation of leptin-JAK2-STAT3 signaling as one pathway that mediates obesity-induced aggressive tumor progression.