April 26, 2010 -- Factors that increase the risk of breast cancer for white women have less influence among women of Hispanic ethnicity, a new study shows.
The finding comes from an analysis of population-based data on about 4,800 white and Hispanic women enrolled in a research project called the 4-Corners Breast Cancer Study.
Known risk factors for breast cancer include reproductive history, family history of breast cancer, menstrual history, hormone use, alcohol consumption, physical activity, height, and body mass index.
Researchers found that:
- 62% to 75% of breast cancer cases among white women were attributed to known breast cancer risk factors, compared with only 7% to 36% of cases among Hispanic women.
- Hispanic women were more likely to have characteristics associated with lower breast cancer risk, such as earlier age at first childbirth, having more children, shorter height, less hormone use, and less alcohol consumption.
- Among premenopausal women, taller height and family history of breast cancer were associated with increased risk in white women, but not among Hispanic women.
- Among postmenopausal women, certain breast cancer risk factors in whites, such as recent hormone therapy and younger age at the first occurrence of menstruation, had no or little association with breast cancer in Hispanics.
The researchers say the findings suggest that many of the risk factors studied up to now explain fewer of the breast cancer cases that arise in Hispanic women compared with white women.
"These differences are likely to contribute to disparities in breast cancer incidence rates and could potentially reflect differences in breast cancer development among these ethnic groups," study researcher Lisa Hines, ScD, of the University of Colorado, says in a news release.
Ethnic differences in genetic, environmental, or lifestyle factors may affect the susceptibility of women to the development of breast cancer.
Estimating Breast Cancer Risk
The researchers also conclude that the study's findings indicate that the use of models to estimate a woman's risk of breast cancer, developed from previous research involving non-Hispanic white populations, needs to be evaluated among other ethnic and racial populations.
Hines says that it is not fully understood why breast cancer occurs more frequently in certain ethnic and racial groups, but that previous studies have shown that white women have a higher incidence of breast cancer than Hispanic women.
Among other conclusions:
- White women had a higher incidence of breast cancer compared with Hispanic women for every age group analyzed. That difference seemed to increase with age.
- Among premenopausal women in the group, a higher proportion of Hispanic women than white women reported characteristics associated with a lower risk of breast cancer, specifically, younger age at first birth, having more children, shorter height, higher body mass index, no oral contraceptive use, and less alcohol consumption.
- Characteristics associated with increased risk that were more likely to be reported among Hispanic women included younger age at first menstruation, not breastfeeding, and low physical activity.
- Older age at first birth was the only risk factor that was associated significantly with increased risk among both white and Hispanic women.
The researchers conclude that their findings "provide support for notable ethnic differences in both the prevalence of risk factors and their associations with breast cancer in comparisons between [non-Hispanic white] women and Hispanic women."
The researchers write that their findings "demonstrate that there are ethnic differences in both the prevalence of established breast cancer risk factors and their associations with breast cancer."
The differences may help explain the disparity in breast cancer incidence rates, and the study suggests more research is needed to pinpoint breast cancer risk factors among ethnic and racial populations.
The study is published in Cancer.