TUESDAY, April 15, 2008 (HealthDay News) -- Although the overall incidence of breast cancer dropped dramatically after millions of American women stopped using hormone-replacement therapy in 2002, that decline doesn't seem to have benefited black women.
In fact, the rates of invasive breast cancer stayed essentially the same for black women from 2002 through 2004, while they were sharply decreasing for whites and Hispanics, according to a study presented April 13 at the American Association for Cancer Research annual meeting, in San Diego.
"In women in the age group from 50 to 69 -- those more likely to use hormone-replacement therapy -- we found that the reduction in invasive breast cancer with estrogen-receptor positive tumors was like 13 percent for whites, 11 percent for Hispanics, about 4 percent for Asian or Pacific Islanders and no change for African-Americans," said the study's lead author, Dezheng Huo, an epidemiologist at the University of Chicago Medical Center.
Huo said several factors could be at play. One is that mammogram screening programs might not be effectively reaching all racial groups. Another factor is that black women have less estrogen-receptor positive cancers, and so the decline in HRT use might not have as dramatic an effect on their cancers, he speculated.
Another reason might be that black women may have used HRT less frequently than white women, and so again wouldn't be as affected by the declining use of hormones. Elizabeth Ward, director of surveillance research for the American Cancer Society, said that at least one past study found baseline use of HRT of about 14 percent of women prior to 2002, compared to only about 10 percent of black women.
When research results from mid-2002 suggested that taking HRT might increase a woman's risk of heart disease and cancer, many women stopped taking these supplements. Almost immediately after women aged 50 to 69 stopped taking HRT, the rates of estrogen-receptor-positive breast cancer began to decline sharply in whites, about 2 percent for every three months during the second half of 2002 and all of 2003, according to Huo. The decline stabilized in 2004. During that same time frame, there was no change for black women. Estrogen-receptor-positive breast cancers are fueled by the female hormone estrogen.
Huo and his colleagues gathered the study data from 17 cancer registries, covering about 26 percent of the U.S. population.
The researchers also looked at the effect of declining HRT use on estrogen-receptor-negative tumors, and found a slight reduction for whites and Hispanics, but a slight increase in black women. According to the researchers, about 80 percent of tumors in white women are estrogen-receptor-positive, compared to about 60 percent in black women. Women from Nigeria, for example, have estrogen-receptor-positive tumors only about 30 percent of the time, according to the researchers.
Ward said it's important to realize that the differences in tumor types might not be due to race, but due to environmental and social factors.
Huo's team also examined the effect of stopping HRT on very early breast cancers, and found virtually no change.
At the end of 2004, there was a slight increase in the rates of invasive breast cancer for Asian/Pacific Islanders, which Huo said might be attributable to an increased rate of mammography in this group of women.
"This is an area of a great deal of interest -- we've known that black women have a lower incidence of breast cancer, but higher mortality rates. No one really understands why," said Ward, who added that all women should get a mammogram every year. "Mammography can detect breast cancer early and can decrease the risk of dying early," she said.
To learn more about what's known about race and breast cancer, visit the American Society of Clinical Oncology.