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What Causes Breast Cancer?
Contrary to e-mail alerts, deodorant and antiperspirant do not cause breast cancer. However, researchers continue to explore and uncover potential causes for the disease.
For decades medical scientists have chased a wide range of provocative clues, seeking the causes of breast cancer. Could the disease be caused by exposure to electromagnetic fields? What about a potential link between the use of underarm deodorants and proliferation of the disease?
Some worried women have even wondered whether it was something they did wrong. Could they have become so stressed that breast cancer was the result?
Rigorous scientific analyses have roundly dismissed the role of electromagnetic fields and deodorants. And doctors constantly discourage patients from assuming that stressed-out lives lead to cancer. Breast cancer is an insidious disease, doctors underscore, with causes unknown. Researchers are now revealing their findings that suggest that certain foods, beverages, hormones, mutated genes and proteins may play roles in the disease's development.
In a series of provocative studies conducted by scientists at the National Cancer Institute and several other institutions in this country and abroad, some solid links to diet and breast cancer have begun to emerge, and some of the most intriguing concern meat preparation.
"It is not the meat but how the meat is cooked," said Dr. Rashimi Sinha, a cancer epidemiologist at NCI in Bethesda, Md., who reported her results about links between meat preparation and breast cancer along with several other scientists at a recent meeting of the American Association for Cancer Research. Meat that is pan-fried, flame-broiled, barbequed or charred at high temperatures can substantially increase the risk of breast cancer, researchers say.
Sinha and a team of scientists at the Iowa Women's Health Study, an ongoing examination of numerous health issues, emphasized that any animal tissue - chicken, fish, beef or pork -- cooked from 300 degrees to 500 degrees Fahrenheit produce suspect compounds now being linked to breast cancer. The targeted compounds, Sinha and other researchers said, are heterocyclic amines, or HCAs. But of the many types of HCAs produced in high-heat meat preparation, one type known as phenylimidazo pyrimidine, or PhIP, is the kind linked to breast cancer.
In the past, HCAs were linked to cancer, but primarily to tumors of the colon. Those studies date back to the 1970s. Discovering new links between PhIP and breast cancer paves the way for preventive measures, scientists say.
Dr. Wolfgang Pfau, a cancer researcher at Hamburg University in Germany, believes he may have uncovered the molecular mechanisms that underlie how PhIP can promote breast cancer. His studies show that PhIP might act as a weak estrogen. Hormones, doctors have long known, can propel tumor growth. Even natural estrogens produced cyclically by the body put a woman at greater risk of breast cancer if she experienced an early menarche and a late menopause. So, it is no surprise that compounds consumed through the diet that act as an estrogen would also increase the risk for breast cancer. Pfau's studies suggest that PhIP binds to the estrogen receptor on breast tissue cells.
Cancer epidemiologist Dr. Kala Visvanathan of Johns Hopkins University in Baltimore, who also has been studying the role of meat preparation and its link to breast cancer, underscored that if further studies reveal PhIP to be a genuine cause of the disease, then it is a risk women can avoid. Alcohol, doctors say, is another avoidable risk. Studies increasingly show, for instance, that women who consume as few as one alcoholic beverage a day are at greater risk for breast cancer than their non-drinking counterparts.
An analysis conducted by Dr. Matthew Longnecker of the National Institute of Environmental Health Sciences found that women who consumed only one alcoholic beverage a day had an increased breast cancer risk of 40 percent. For those who consumed a minimum of two drinks a day the risk was 70 percent. But even with such elevated risks, Longnecker's study found that only 4 percent of all cases of breast cancer could be linked to alcohol.
So what explains the rest?
Scientists are convinced there will never be a simple explanation for all cases of breast cancer. In other words, the evolving studies on meat preparation and alcohol consumption do not come close to explaining why breast cancer is so prevalent.
The disease strikes 182,000 women annually in the United States and claims the lives of 46,000. And just as there are influences such as diet, hormones and alcohol consumption, there are other subtle mechanisms, such as genes, that can lead to the disease.
Even though fewer than 10 percent of breast cancer cases that occur annually can be linked to mutated genes, aberrant genes trigger a cascade of molecular events that drive the uncontrolled growth of cells in breast tissue, leading to tumor development. Scientists around the world are trying to identify all of the mechanisms in which genes influence tumor development and growth. Two key genes, BRCA1 and BRCA2, have been linked to breast cancer and are prominent in families where the disease is passed from one generation to the next.
Here is a summary of what doctors know about BRCA1 and BRCA2:
BRCA1 is what is known as a tumor-suppressor gene, but can be mutated in certain families and thus can lead to breast and ovarian cancers. An estimated 5 percent of all breast cancers are associated with a mutated BRCA1 gene. Families with the BRCA1 mutation, studies also show, tend to develop breast cancer at an early age, usually before 50. Many of these cancers occur in women in their 20s and 30s. The risk of developing breast cancer by age 80 is greater than 80 percent for carriers of this gene, which is located on chromosome 17.
BRCA2 is responsible for about 4 percent of all breast cancers and is also linked to male breast cancer. People with the BRCA2 mutation are also likely to develop the disease before age 50.
While the incidence of ovarian cancer is estimated to range between 20 percent and 60 percent for women with the BRCA1 mutation, the incidence of ovarian cancer for women with BRCA2 is far less, about 10 percent to 20 percent. BRCA2 is found on chromosome 13. Of those familial breast cancers, approximately 40 percent are linked to BRCA1 and another 40 percent of the remaining familial cancers are linked to BRCA2. This leaves a fair percentage of cases attributable to an undiscovered gene or group of genes: a possible BRCA3. No such gene has been discovered yet.
Meanwhile, scientists from Technical University in Munich, Germany, have found that as much as 45 percent of breast cancer patients have an elevation of two key proteins in tumors. One of those proteins is known as uPA, or urokinase-type plasminogen activator. The other is PAI-1, the natural inhibitor of uPA.
Whether uPA is involved in triggering the disease or whether it becomes elevated once a tumor develops has yet to be determined. However, scientists know this much: uPA is key in the spread of breast cancer, a factor strongly suggestive of the protein's role in influencing the process of cancer growth.
Dr. Anita Prechtl, the study's lead investigator, looked at 684 women whose tumors measured up to 5 centimeters in diameter but had not metastasized to adjoining lymph nodes. She believes that by first testing for the presence of the proteins, doctors can more precisely determine the dose and duration of chemotherapy for breast cancer. In fact, if women diagnosed with breast cancer are screened for the proteins in their initial work-up for the disease, many can be spared unnecessary chemotherapy based on blood levels of the proteins. Such screening, Prechtl said, is under way throughout Europe.
Dr. Karen Antman of Columbia Presbyterian Medical Center in Manhattan cautioned, however, that the test needs further confirmation in larger studies before it can be widely used as a diagnostic for breast cancer.
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