May 5, 2008--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.

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."

Part of the confusion isn't a black thing. In general, no one understands exactly what causes breast cancer or why seemingly healthy women who are "doing everything right" still get it.There are also no absolute answers for how to prevent it — though there are factors that raise the risk. Along with age, according to the American Cancer Society, these are several other breast cancer risk factors:

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.

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.