The literature search was conducted using the PubMed electronic database by searching the following keywords: leptin or obesity AND cancer, leptin or obesity AND colorectal cancer, leptin or obesity AND glioma, leptin or obesity AND lung cancers, leptin or obesity AND breast cancer, leptin or obesity AND colorectal cancer, obesity AND cervical cancer, obesity AND ovarian cancer, leptin or obesity AND cancer of the corpus uteri, leptin or obesity AND endometrial cancer. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.