Anemia: a defense against cancer?

Scientists have long suspected that iron plays a role in cell proliferation processes, such as cancer. Now, University of Florida-Gainesville researchers have shown that supplemental iron can enhance tumor growth in laboratory animals, and they suggest that anemia may be a defense mechanism in cancer patients.

The researchers injected leukemia cells into mice treated with iron at levels "comparable to clinical doses for humans" and into untreated mice. They found that tumors grew faster in iron-treated mice and that these animals succumbed to the disease faster than did untreated animals.

Most living things, from microorganisms to cancer cells, need iron to grow, says Raymond J. Bergeron, who directed the research. When bacteria invade the body during an infection, the body removes iron from the bloodstream and "hides" it in the liver, making it unavailable for bacterial growth. Such a mechanism might also take place in certain cancers and explain why many cancer patients have anemia, according to the report in the March JOURNAL OF NUTRITION.

Indirect evidence for anemia's role as a defense against cancer abounds. For example, the researchers note, people with hemochromatosis, a disease of iron overload, often die of cancer; South African Bantus, who drink beer brewed in iron pots, have a high incidence of liver cancer; and tumors often develop at sites of iron injection in animals and people.

Bergeron reported in an earlier study that iron chelators -- molecules that tightly bind iron--prevent it from being incorporated into ribonucleotide reductase, an iron-dependent enzyme that catalyzes a step of DNA synthesis. Because cancer cells require rapid DNA synthesis to multiply, iron chelators slow cancer growth. The mechanism partly explains how anticancer drugs work, although scientists didn't realize it for many years, Bergeron says.

The researchers warn against extrapolating the results of the present study to humans. "We were really reticent to publish the results because the implications are incredible," Bergeron says. "We don't want people calling and asking us 'Am I going to get cancer from taking [iron supplements]?"

Bergeron and colleague Richard R. Streiff, a hematologist, answer with an emphatic "no," explaining that iron has never been shown to cause cancer. For cancer patients who war taking iron supplements, the current mode of clinical therapy should not be changed, they add. The study involved only one type of cancer--mouse leukemia--and, they note, "different cancers have different biochemical requirements."