"Nutrient depletion" is how Dr. Ed Harris, Texas A&M University biochemist, describes the process in the February issue of Nutrition Reviews. His article traces how independent studies around the world led researchers to consider copper, a trace mineral in the human diet, for its potential in controlling cancerous growth.

"The idea is to deprive a selective nutrient from being active in tumors. In research so far, there is no indication of anyone being cured, but tumors have stopped growing," said Harris, who is an expert on the relation of copper in various human diseases. "Ultimately, nutrient depletion may be used in combination with other treatments."

The role of copper to control cancer traces its beginnings to Dr. Judah Folkman of the Harvard School of Medicine, whose pioneering work in angiogenesis, or the formation of new blood cells, began about 40 years ago but only since the 1980s have been recognized in medical research. Folkman first launched the idea that if a tumor is to grow, it must have its own blood supply, Harris said.

"For one increment of tumor growth, Folkman said, there also must be one increment of capillary or vessel growth," Harris noted. "And that was shocking."

But that astonishing notion led some researchers to explore ways to stop the capillary growth that nourished tumors. About the same time, other researchers were examining the role of copper in forming blood vessels.

To test a theory of whether copper was instrumental in blood vessel formation, scientists needed an organ that had none. They found that in the cornea of rabbit's eyes. Small pellets of copper were implanted into rabbit corneas, and soon vessels formed around them, the biochemist noted.

Then came the idea that if copper was needed to create blood vessels, and if blood vessels were necessary for tumor growth, what would happen if copper were regulated?

"Studies looked at inoperable cancer -- cancer that couldn't be touched as in deep in the brain," Harris said. "There was some impact, but there also was fear that perhaps such treatment would stop the cancer but cause a serious copper-deficient disease."

Yet another study, by George Brewer in Michigan, looked at the use of tetrathiomolybdate, which is normally given to people with a copper overload, Harris said.

Brewer got permission to try the anti-copper drug on terminal cancer patients for six months in an attempt to lower their copper levels and thus stop the blood-vessel growth that was feeding the tumors. "Five of the six people who received the drug showed no further growth in their tumors after one year," Harris noted. "And it was found that cancers of the muscle don't respond to this treatment. But even that is encouraging because it narrows down and gives researchers a place to look to see what is different about cancers of the muscle and blood vessel supplies."

Harris said every drug ever made has been tested against cancer, but nutritional intervention may lead to a different approach in combination with other medical treatments.

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