Amongst all its other health benefits, calorie restriction appears to also reduce the risk of certain types of cancer: "A restricted-calorie diet inhibited the development of precancerous growths in a two-step model of skin cancer, reducing the activation of two signaling pathways known to contribute to cancer growth and development ... An obesity-inducing diet, by contrast, activated those pathways ... These results, while tested in a mouse model of skin cancer, are broadly applicable to epithelial cancers in other tissues ... Epithelial cancers arise in the epithelium - the tissue that lines the surfaces and cavities of the body's organs. They comprise 80 percent of all cancers. ... Calorie restriction and obesity directly affect activation of the cell surface receptors epidermal growth factor (EGFR) and insulin-like growth factor (IGF-1R). These receptors then affect signaling in downstream molecular pathways such as Akt and mTOR. ... Calorie restriction, which we refer to as negative energy balance, inhibits this signaling, and obesity, or positive energy balance, enhances signaling through these pathways, leading to cell growth, proliferation and survival."