Cadmium and prostate cancer

Prostatic cancer is a common and frequently lethal malignant disease. In the United States and other countries the incidence and mortality rate of prostate cancer continue to rise. Cancer of the prostate has an extremely complex etiology and appears dependent on a variety of factors, making linkage to a single factor very difficult to detect. Cadmium is a metallic toxin of great environmental and occupational concern. Cadmium exposure has been associated with human prostatic cancer in some, but not all, epidemiologic studies. Some studies indicate that tissue levels of cadmium in the human prostate correlate with malignant disease. Any association between cadmium and prostatic cancer has been controversial, in large part because of a previous lack of relevant animal models. However, several chronic studies in rats revealing a correlation between cadmium exposure and prostatic tumors have been published over the last several years. These include a study of oral cadmium exposure, a route extremely relevant to human exposure. Several of these chronic studies indicate a hormonal dependence of cadmium-induced prostate cancer. Other supportive work continues to accumulate, such as studies showing in vitro malignant transformation of prostatic epithelial cells with cadmium exposure. In addition, there are indications that the primary biologic tolerance system for cadmium (i.e., the metallothionein gene) may be only poorly active in the specific lobes of the rat prostate in which cadmium induces tumors. The induction in rats of prostate cancer by cadmium treatment clearly supports, but does not definitively establish, a possible role for cadmium as an etiological agent in human prostate cancer. Further research, however, will be required to establish the precise role of cadmium in this important human malignancy.