Leptin is a 16 kDa adipocyte-derived hormone, and it has attracted interest in the field of obesity research due to its role in the regulation of energy balance. Leptin, secreted from adipose tissues in proportion to the fat store, acts in the hypothalamus to regulate feeding behavior. leptin has also been shown to play an essential role in tumorigenesis, tumor progression, and metastasis, due to its oncogenic, mitogenic, pro-inflammatory, and pro-angiogenic actions. Mutations in this gene and/or its regulatory regions cause severe obesity, and morbid obesity with hypogonadism. Leptin has also been linked to type 2 diabetes mellitus development.