Loss of muscle mass (scientific term: cachexia) affects about 80% of patients with advanced cancer and impacts their prognosis by decreasing tolerance and response to treatment, decreasing quality of life and survival. The prognosis in these patients depends directly on the importance of the loss of muscle mass. Preserving it is therefore an essential therapeutic objective. It is therefore important to understand perfectly the mechanism of this muscular loss. The accumulation of fat in the muscle (scientific term: myosteatosis) could be a mechanism responsible for this loss of muscle mass. It is indeed a hypothesis proved on animal models. Moreover, it has recently been shown that more the cancer patient loses weight, more his muscle contains fat. This lets think that this deposit of fat in the muscle would be directly related to the loss of muscle mass. All of these observations could not be clearly established in humans and investigators are seeking by this study to illuminate these mechanisms at the human level. A better understanding of these mechanisms would allow investigator to set up targeted treatments against the accumulation of fat in the muscle, which would significantly improve the quality of life of patients with cancer of the aerodigestive pathways and their chances of recovery.