Cancer cachexia is characterized clinically by anorexia, early satiety, weight loss, anemia, and marked asthenia. The syndrome is not the result of semi-starvation alone but it represents a complex metabolic problem. In the host there are abnormalities in metabolism of energy, carbohydrate, lipid and protein, in water content, in acid-base balance, in electrolyte, mineral and vitamin concentrations, alterations in the activity of host tissue enzymes and changes in endocrine homeostasis and immunologic mechanisms. The cancer initiates and contributes to the genesis of the syndrome but complications of the disease and the treatment may also play a role. Only the control of the cancer can reverse completely the syndrome. It was proposed that cancer peptides throw the host metabolism into a chaotic biochemical state by activating and inactivating host enzymes. This results in increased energy expenditure; the released host metabolites are trapped by the growing cancer.