Pathophysiology of cancer cachexia: current understanding and areas for future research.

Weight loss and failure to gain weight normally in cancer patients are attributable to negative energy balance and altered metabolism. Energy balance is negative because of decreased intake, increased expenditure, or both. Changes in carbohydrate metabolism include glucose uptake and lactate production by tumor, relative hypoinsulinism, and relative insulin resistance. Alterations in protein metabolism include preferential uptake of amino acids by the tumor, decreased synthesis of some host tissue proteins such as muscle tissue, and increased synthesis of other host proteins. Lipid metabolism is seemingly less affected. These metabolic changes result in muscle wasting in adult cancer patients and growth failure in pediatric cancer patients. Host tissues are catabolized to meet the nutritional demands of tumor, and nutritional death may ensue.