Monday, May 14, 2007

Not to your health: new mechanism proposed for alcohol-related tumors

A glass of wine may be good for the heart-but may promote some cancers. Scientists have now figured out what's behind that sobering observation. New findings suggest that alcohol encourages blood vessels to infiltrate and nourish nascent tumors.

Researchers have long known that drinking alcohol is a risk factor for stomach, liver, and breast cancers, among others. Previous studies prompted a host of theories--for example, that heavy drinking displaces other nutrients in the diet or that acetaldehyde, a metabolite of alcohol, acts as a carcinogen--but they haven't clarified the alcohol-cancer connection.

Seeking an explanation, Jian-Wei Gu and his colleagues at the University of Mississippi Medical Center in Jackson inoculated chick embryos with human fibrosarcoma cells, derived from a type of bone cancer. Since chick embryos support human-cell growth and can be monitored through a window cut into their shells, they are frequently used for studying cancers that grow in people.

Gu's group dosed some of the embryos for 9 days with an amount of alcohol corresponding to about two glasses of wine a day in people. Other embryos received a saline solution instead. They were all then observed for 17 days.

In the embryos given saline, only a few new blood vessels infiltrated the tumors, which grew only slightly. However, tumors in the alcohol-treated embryos developed an extensive network of blood vessels, a process called angiogenesis, and doubled in size.

Further examination showed that cancer cells in the alcohol-dosed embryos, unlike their saline-only counterparts, secreted a protein called vascular endothelial growth factor. This protein, Gu's team notes in the Jan. 15 Cancer, probably signaled blood vessels to grow into the embryos' tumors.

Gu says that a similar mechanism might encourage the growth of tumors that spontaneously arise in people. The immune system regularly kills off small tumors before they acquire blood vessels. "Without blood vessels, cancer can't grow very fast" he says. "If something [such as alcohol] promotes tumor angiogenesis, it's a very important mechanism for cancer growth."

Judah Folkman, a cancer researcher at Harvard Medical School in Boston, says that Gu's hypothesis "sounds logical" but must be tested in people. If it proves correct, the finding may put a damper on current recommendations to have a daily drink to promote heart health (SN: 3/8/03, p. 155). "The question is, At what level would it be counterproductive for people who are at risk for cancer?" says Folkman.

For now, Gu proposes a prudent approach to drinking: "If you're healthy and of legal age, drinking a little bit is fine. But we believe if a person has a high risk of cancer, they shouldn't drink."

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