A critical evaluation of the role of trace elements in human cancer

The interest in the role of trace elements in cancer is increasing, particularly for those with a possible protective action, such as Se and Zn. Despite the vast amount of investigations already conducted, there is a need for further epidemiological studies to better understand what compounds, at what levels, and with which mechanism trace elements are involved in protection against a specific cancer type or groups of cancer. Critical aspects remain the search for the most appropriate biological indicators of body burden, the variability in biological activity according to chemical form and the current state of knowledge of the mechanisms of action which could be mediated by interference of the neuroendocrine and/or immune system. On the basis of our experience on the relationship between trace elements and cancer disease, we discuss the critical aspects of the problem and try to define guidelines for future research.