LEP and obesity due to melanocortin 4 receptor deficiency: But, obesity appears to be associated with the development of differentiated thyroid cancer, particularly with leptin, a hormone produced primarily by adipose tissue; leptin and its receptor (OB-R) have been implicated to be overexpressed in thyroid carcinomas, particularly papillary thyroid cancer, as multiple studies of PTC tissues have shown an expression of 50–80% of PTC tissue expressing OB-R and leptin [21,22,23,24].