DNC News

Cadmium fuels tumor growth rates......

[ This article was copied from a newsletter sent out by Great Smokies Diagnostic Laboratory to promote their test for heavy metal toxicity ].

"If you drink much from a bottle marked 'poison,' it is almost certain to disagree with you, sooner or later." "Lewis Carroll (1832-1898), Alice in Wonderland, 1865

Where there's fire, there's smoke - and where there's smoke, there's cadmium - a toxin commonly found in cigarette smoke and fossil fuel emissions, as well as other sources such as animal liver, shellfish, municipal waste, and drinking water.

Cadmium has been shown to trigger cancerous tumor growth in cultured cells and in laboratory rodents. But now scientists have found that the effects of the toxin on tumors may be even more long-ranging and pervasive than originally thought.

According to a new in-vivo study by researchers from the National Cancer Institute at the National Institute of Environmental Sciences and the Department of Pathology at the University of Western Ontario, cadmium appears to act as a "fertilizer" that stimulates the growth and spread of malignant tumors in rats exposed to repeated doses of the toxin.

Injections of cadmium increased the number of tumors that metastasized to other parts of the body, including the lung, lymph nodes, and liver. In most human cancer cases, the scientists noted, tumor metastases are more likely to prove fatal than the primary tumor itself. "It is obvious that human populations, during an average lifetime, would experience repeated exposure to Cd [cadmium]," researchers observed. Cadmium has a long biological half-life and accumulates in the body with persistent exposure. Cigarette smoking, for example, roughly doubles a person's lifetime body burden of cadmium.

Curiously, initial exposure to low-doses of cadmium in rats seems to afford some degree of protection against overt symptoms of acute toxicity, such as lung damage, when they are exposed to larger doses later. Yet this low-dose exposure, while protective in the short term, ultimately fuels more aggressive cancer spread and progression, possibly by interfering with the cells' natural life cycle.

Scientists theorized that an initial low-dose exposure might damage the DNA in cells and interfere with the natural "suicide" mechanism, called apoptosis, of the cells. While the mutated cells might provide some degree of tolerance against the immediate symptoms of acute toxicity, the fact that they would continue to survive with genetic damage would be more likely to spur malignant growth. These experimental results indicate that "repeated exposures to the carcinogenic, inorganic Cd can result in the more rapid onset of more highly aggressive tumors," the researchers concluded.

Sources: Waalkes MP, Rehm S, Cerian MG. Repeated cadmium exposures enhance the malignant progression of ensuing tumors in rats.

Toxicol Sci 2000;54:110-120.
Available full-text during a free trial period at:
Agency for Toxic Disease Registry
Cadmium ToxFaq

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