The metabolic environment of cancer.

The tumor cell has a very distinctive metabolism. It acts as a metabolic trap for host nutrients thus taking vital compounds for the metabolism of the host. Depending on the particular tumor growing pattern, cancer cells use preferentially glucose or amino acids for their energetic or biosynthetic needs. Lipids, fatty acids in particular, can also be taken up by the tumor cell. In addition, it can also release some compounds into the host circulation which are not normally produced by the original cell before neoplastic transformation. Some of these compounds affect the metabolism of the host in an unfavorable way since they can oppose the host's metabolic responses, which sustain homeostasis. The final product is that the metabolic machinery of these cells allows them to grow continuously in an uncontrolled manner. The consequences of tumor invasion on the host's metabolism are varied. They have, however, one thing in common: the reduction of the metabolic efficiency of the host. Muscular protein depletion, increased gluconeogenesis, uncoupling of oxidative phosphorylation constitute the main metabolic responses of the host as a result of tumor invasion. The net result of all these metabolic changes is profound energy imbalance which normally ends with cachexia and, eventually, death.