HACKENSACK, N.J. — Thousands of women are helping scientists learn more about breast cancer in African-Americans, including why it strikes young black women more aggressively and more often than white women.

They are answering a host of lifestyle questions, providing saliva samples for genetic analysis, and allowing researchers to measure their body mass index as part of the most ambitious project to date to understand why breast cancer affects women of different races differently. More than 2,400 New Jersey women have joined the study already.

When these participants are combined with those from three other studies nationally, more than 10,000 women — half of them diagnosed with cancer and half of them healthy "controls" — will have participated. The National Cancer Institute provided $19.6 million in added funding this summer to allow four separate regional studies to pool their data, making it the largest study of its type.

"Breast cancer in African-American women occurs at an earlier age than in European-American women," according to the first paper from the Women's Circle of Health study, which began in 2003. It was co-authored by Dr. Elisa V. Bandera of the Cancer Institute of New Jersey and Karen Pawlish of the New Jersey Department of Health and Senior Services, with 28 others.

Black women are more likely to have high-grade tumors and tumors that don't respond to hormonal therapy, the study has found. But the reasons are unknown, the 2009 report said.

Ethel Spray of Teaneck, N.J., wants to help find out why. Diagnosed last year, she has fully recovered. "When I got the letter (about the study) this past May, I responded to it," she said. An interviewer visited her and asked about "the type of food you eat, what you drink," she said. "Sometimes it's something in your past, stress that could bring it on."

"If there's any type of research or study that can make a difference in anybody's life, I would like to see it done," Spray said.

To find cancer patients for the study, the state health department culls the New Jersey State Cancer Registry, to which all new diagnoses are reported by doctors, hospitals and laboratories. State health department staff call them and explain the study, said Pawlish, a state researcher. Those who agree to join are interviewed at their homes by Cancer Institute staff for about two hours.

This fall, Bandera, the principal investigator in New Jersey, will start evaluating the role of diet and obesity on breast cancer in African-Americans.

Earlier studies established a link between obesity and breast cancer in postmenopausal women, but they focused primarily on white women, she said.

"The impact of obesity on breast cancer risk among African-American women is not well-known," she said.

The findings so far are provocative: Among women with breast cancer, 52 percent of African-Americans in the study were obese, compared with 26 percent of whites.

The study will also be able to look at some rare types of breast cancer "that are more common in African-Americans," Bandera said, including triple-negative breast cancer and inflammatory breast cancer.

The large pool of data formed by combining the Women's Circle of Health Study in New Jersey and New York with three other studies nationally means scientists will have enough women with these rarer subtypes to make valid conclusions about their relationship to various risk factors and genes.

Black women overall are more likely to die from breast cancer, when all ages are considered. Scientists have found there's more at work than differences in income, health insurance and access to health care.

"We found that African-American women were 70 percent more likely to die of breast cancer, compared to white women with breast cancer," said Pawlish, who analyzed earlier registry data for a paper on cancer survival disparities.

Even after controlling for the poverty level of each patient's neighborhood, "African-Americans still had a worse survival rate," she said. "They were about 43 percent more likely to die."

Determining what environmental, genetic and lifestyle factors contribute to this disparity is the researchers' next challenge.

"I've been finding it (breast cancer) more and more in much younger women, since I've been doing this," said Cheryl Walters, a 14-year survivor who is president of the Bergen-Passaic chapter of Sisters Network, a national organization of African-American breast cancer survivors.