[Trace elements: mechanistic aspects of anticarcinogenic action]

Trace elements play important roles and are increasingly recognized as versatile anticarcinogenic agents. Several biologic mechanisms have been proposed to explain how trace elements could reduce the incidence of a number of different cancers. The proposed mechanisms involve the antioxidant potential of trace element dependent enzyme system, induction of metallothionein, effects on immune response and DNA repair system, alterations of carcinogen metabolism, and apoptosis of the initiated cells. However, epidemiologic studies have failed to support the hypothesis that enhanced trace element status reduces the risk of cancer. Furthermore, several animal and in vitro studies have shown carcinogenic potentials of trace elements. A few chemoprevention trials with trace elements have now been conducted.