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Last year, when "Good Morning America" anchor Robin Roberts found a lump in her breast during a self-exam, her first thought was: This can't be; I'm too young! Yes, at 46, Roberts was younger than age 55, when two out of three invasive breast cancers are diagnosed. But she's also black.

Though African-Americans are less likely than white women to get breast cancer, when we do get it, the disease strikes younger and is more deadly. And black women have a higher risk of developing and dying from breast cancer than Asian, Hispanic or Native American women.

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More chilling, over the past several years, many studies have shown that compared to other women, African-American women are more frequently diagnosed with an aggressive form of breast cancer that resists some kinds of treatment. This type of tumor also occurs at younger ages, often before age 35. Last summer, researchers at the University of North Carolina identified a specific, virulent breast cancer tumor that strikes young black women 10 times more often than either white women or even older black women. Moreover, our tumors are generally diagnosed and treated later in the game, which makes them especially dangerous.

Happily, Robin Roberts is doing just fine and is back on the air. She caught her cancer early and received treatment quickly. She has become an outspoken breast cancer role model and activist. In fact, last month she shed her wig and now proudly displays her post-treatment hair — cute and very short. She and other survivors across the country have helped shine the light on the enigma of breast cancer in black women and increase the pressure on scientists to solve this mystery.

And it is a mystery. No one can fully and clearly explain the black-white differences in breast cancer, particularly the more aggressive, lethal form of the disease that black women are likely to contract. Is there something different about our genetic makeup that makes us susceptible to a cancer that doesn't respond to treatment and kills fast and young? Is it our environments — that so many of us live in disadvantaged communities, where stress, poverty and pollution are simply a part of everyday life and healthy food and quality medical care are not? Is it racism — could it be that it's not breast cancer that discriminates, but an unequal health care system and the people who run it?

According to experts, there is no one answer, but a thorny tangle of questions.

"We know that African-American women are more likely to have tumors that are more aggressive and less responsive to treatment," says Dale Sandler, chief of the Epidemiology Branch at the National Institute of Environmental Health Sciences and principal investigator of the Sister Study, a large research project that is looking at breast cancer by focusing on women who have lost sisters to the disease. "We also know that black women either delay seeking treatment or get the runaround when they do. Still, these factors don't account for all of the disparity in mortality. Clearly something else is going on."

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Family History/Genetics: Breast cancer risk is higher among women whose blood relatives have the disease. Having one first-degree relative (mother, sister or daughter) with breast cancer doubles a woman's risk, and two first-degree relatives increases the risk about fivefold. Five to 10 percent of breast cancer cases are believed to be inherited, a result of gene changes or "mutations" inherited from a parent . The most common inherited mutations are those of the genes known as BRCA1 and BRCA2.

Exposure to Hormones: During the childbearing years — from puberty to menopause — a woman's body produces estrogen. This female hormone is important for normal sexual development and functioning of the female reproductive system. However, higher levels of circulating estrogen are associated with an increased risk of breast cancer. Which means that women whose periods start early in life or end later, or those who have their children later, have fewer or no children, drink more alcohol or take hormone replacement therapy increase their lifetime exposure to estrogen and raise the risk of breast cancer.

For black women, exposure to estrogen doesn't fully unravel our breast cancer puzzle. On one hand, as a group, we are exposed to less estrogen because we have more children, have them earlier in life and use hormone replacement therapy less than white women. On the other hand, our periods start earlier — which means more estrogen. Additionally, after menopause, when the ovaries no longer produce estrogen, body fat is the primary source for estrogen made by the body. Black women are more likely to be overweight and have more body fat, which equals more estrogen.

The bottom line, says Sandler: "What we know about hormones doesn't explain it all. When you put everything together, hormones and reproductive history only explain about 50 percent of breast cancer overall. And even that estimate is based on studies of mostly white women," she adds. "It might be different for black women."

The Environment: Very little is known about the link between environmental factors and the risk of breast cancer. But there's plenty of speculation. "What is accounting for the rest of breast cancer?" asks Sandler. "Is it chemicals a woman's exposed to at work? Something in our food or water? Pesticides? Those plastic bottles we've been reading so much about? We don't know yet, but we'd like to find out."

The Sister Study should answer some of these questions, says Sandler. Conducted by the National Institute of Environmental Health Sciences in North Carolina, the study is enrolling 50,000 diverse women whose sisters had breast cancer. Sandler and her team hope to learn how environment and genes affect the chances of getting the disease.

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Across the country, other researchers are also committed to studying black women and breast cancer. In 2005, Dr. Olufunmilayo Olopade, a Nigerian oncologist and director of the Center for Clinical Cancer Genetics at the University of Chicago Medical Center, won a prestigious MacArthur "genius grant" of $500,000 to continue studying the genetics of breast cancer in women of African heritage. Dr. Lisa Newman, director of the Breast Care Center at the University of Michigan Comprehensive Cancer Center, is another black woman on the frontlines of breast cancer research.

As science works to figure out what causes breast cancer and strives to understand the disease in black women, our most effect weapon against it remains early detection.

The American Cancer Society and other organizations recommend the following screening guidelines:

  • Mammograms every year starting at age 40.
  • Women under 40 with a family history of breast cancer or other concerns should talk with a health care provider. Screening tests may be needed more often or started earlier.
  • Clinical breast exams by a health care provider at least every three years starting at age 20, and every year after 40.
  • Breast self-exams every month starting by age 20.

If you have been diagnosed with breast cancer, know that it's not a death sentence and seek support and information. Contact Sisters Network Inc. at http://www.sistersnetworkinc.organd the Susan G. Komen Breast Cancer Foundation at www.komen.org.

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Linda Villarosa is a health columnist for The Root. "Passing for Black" is her first novel. For more go to her Web site.