Washington, DC Researchers at Georgetown University Medical Center have discovered that vitamin A, when applied to breast cancer cells, turns on genes that can push stem cells embedded in a tumor to morph into endothelial cells. These cells can then build blood vessels to link up to the body's blood supply, promoting further tumor growth.
They say their findings, published in the July 16 online issue of PLoS ONE, is a proof of principle of the new and controversial "vasculogenic mimicry" theory, proposing that, as needed, tumors build their own blood pipelines. This is very different from the well-accepted role of tumor angiogenesis, when tumors send signals to blood vessels to grow toward the cancer.
The study's senior author, Stephen W. Byers, Ph.D., a professor of oncology and cell biology at Georgetown's Lombardi Comprehensive Cancer Center, also says that this study helps explain why retinoids-- natural or synthetic vitamin A agents--have had mixed results in treating cancer. "Finding that vitamin A may cause some breast cancer cells to form blood vessels brings up the rather disturbing notion that treatment with these drugs may actually stimulate tumor growth," says Byers.
For example, use of beta-carotene, the most important dietary precursor of vitamin A and the chemical that makes carrots orange, has been found to increase lung cancer progression in a large clinical trial. Additionally, fenretinide, a synthetic retinoid, appears to reduce the risk of second breast cancers in premenopausal women, but increase the risk in postmenopausal women, Byers says.
"None of this means that people should avoid foods rich in vitamin A, or should refuse to take their vitamins," he says. "What led us to this study is that previous research on retinoids implied that they may be effective in a preventative setting, but may actually have a negative effect after tumor initiation and during progression."
|Contact: Karen Mallet|
Georgetown University Medical Center