A combination of anti-hormone therapies seems to show promise in battling some breast cancers, said a prominent researcher visiting the Medical College of Georgia.
Research at MCG is looking at a combination of tamoxifen and the abortion pill RU-486 that seems to have the effect of killing breast cancer cells, which researchers hope might overcome controversy surrounding RU-486.
Dr. Kathryn B. Horwitz, professor of medicine at the University of Colorado Health Sciences Center, spoke Monday as part of the Thomas G. Muldoon Memorial Lecture Series at MCG. Dr. Horwitz gained prominence when she showed that some breast cancer cells have receptors for progesterone, and tests for those receptors are now routinely done on tumor biopsies.
About a third of breast cancers are hormone dependent, meaning they are fueled by hormones such as estrogen and progesterone, Dr. Horwitz said.
"We know that these hormones - that are very important for women and make them women - are also somehow involved in the development of breast cancer," Dr. Horwitz said. "And estrogen is the one that gets most of the attention, but progesterone, I believe, can play a role, too."
Anti-estrogen drugs such as tamoxifen bind to estrogen receptors on cancer cells and prevent estrogen from stimulating the cell. A major five-year study found that tamoxifen can reduce breast cancers in high-risk women by 45 percent.
Although the results are encouraging, there were still women who got breast cancer while taking tamoxifen, where tamoxifen seemed to fuel the tumor, Dr. Horwitz said. And in some women, particularly those with advanced breast cancer, tamoxifen resistance develops, said Dr. Horwitz, who is studying the resistance mechanisms.
Enter the anti-progestins and research such as that done at MCG by Pat Schoenlein, associate professor of cell biology and anatomy, and Thomas Ogle, professor of physiology, who both also work in the Department of Surgery.
Combining RU-486 and tamoxifen had a dramatic impact on human breast cancer cells transferred to mice. The researchers are now looking at a protein involved in regulation of the cell cycle that may be the key, Dr. Schoenlein said.
"It is activated in a synergistic fashion by these two agents," Dr. Schoenlein said. "We 're trying to understand the mechanism to provide more support for the combination therapy."
RU-486, also known as mifepristone, was approved by the Food and Drug Administration but remains a controversial agent even though the cancer researchers aren't interested in its abortion-inducing qualities.
"The research in anti-progesterone therapy is far, far behind, to some extent for political reasons," Dr. Horwitz said. "But there are now newer drugs that maybe don't carry the baggage RU-486 does."
Even so, clinical trials in humans are probably years away and more likely to occur first in Europe, Dr. Horwitz said. Making the case for its impact on breast cancer could help, Dr. Ogle said.
"If our data is dramatic enough, it can move along a little faster," he said.
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