Different from many other liver cancer cell lines, such as Hep3B, Huh7 and HA22T/VGH, HepG2 cells are poor host cells for supporting replication of hepatitis B virus or hepatitis C virus [34–36], and thus is appropriate for studying the interaction of obesity hormone leptin and estrogens in liver cancer cell growth. Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.