LEP and obesity due to melanocortin 4 receptor deficiency: The HFD has been shown to promote tumor progression in the small intestine of genetically susceptible K‐ras G12D mice, independent of obesity.[244] In the context of melanoma, microbiota from leptin‐deficient (ob/ob) or adiponectin‐deficient (AdpKO) mice can stimulate melanoma development in lean wild‐type (WT) mice fed an HFD.[245] Furthermore, the HFD facilitates the formation of a lung pre‐metastatic niche and metastasis.