Breast Cancer Risk Varies Among Mexican-Born and American-Born Hispanics

Roxanne Nelson

February 09, 2009

February 9, 2009 (Carefree, Arizona) — Hispanics are the fastest growing minority group in the United States, but information about their risk for breast cancer is limited. Preliminary data presented here at the American Association for Cancer Research Conference on the Science of Cancer Health Disparities shows similarities and differences in various risk factors among Mexican-born Hispanics and American-born Hispanics.

Researchers found that breast cancer patients in Mexico were significantly older at diagnosis, compared with Hispanics living in the United States. Women in Mexico had a higher number of live births, but other reproductive data, such as age at menarche, menopause, and first pregnancy, were similar between the 2 groups.

The data were drawn from the ELLA Binational Breast Cancer Study, a multicenter collaboration that is being conducted to investigate differences in epidemiologic and clinical risk factors, as well as standard and novel tumor markers, between women in Mexico and Mexican-American women living in the United States.

"We have been able to look at risk factors of women on both sides of the border, and we are comparing a variety of clinical factors and reproductive factors," said Elena Martinez, PhD, professor of epidemiology at the University of Arizona Mel and Enid Zuckerman College of Public Health, in Tucson, and a coinvestigator of the ELLA study.

Until recently, breast cancer was rare in Mexico, and the country was considered low risk for the disease. Although the incidence of breast cancer is still less than half of what it is in the United States, it has become the most commonly diagnosed cancer among women residing in the more industrialized states in Mexico and in the northern regions of the country. Researchers have also observed similar trends toward increasing incidence among women of Mexican descent in the American population, although published literature is somewhat limited.

Speaking at a press briefing, Dr. Martinez explained that data from the ELLA study will help in understanding the burden of breast cancer in populations on both sides of the border.

Thus far, a total of 652 women have been recruited into the study (309 in the United States and 343 in Mexico); the goal is to enroll 1000 women. Both groups had a similar age at menarche (12.8 vs 12.8 years), at menopause (46.5 vs 45.3 years), and at first pregnancy (23.6 vs 22.3 years).

"Obesity in both countries was extremely high," said Dr. Martinez, "and that is a risk factor for many health problems."

The major differences observed to date between the 2 populations are that women in Mexico were significantly older at diagnosis than those in the United States (53.8 vs 48.7 years), had a higher rate of live births (3.7 vs 3.2), and had a higher proportion of triple-negative breast tumors (28.1 vs 19.3%). The prevalence of a family history of breast cancer, however, was significantly higher in the United States (18.1%) than in Mexico (6.2%).

Differences in Risk Factors Among American- and Foreign-Born Hispanic Women

In a related study, Esther John, PhD, a research scientist and epidemiologist at the Northern California Cancer Center, in Fremont, compared known breast cancer risk factors in foreign-born Hispanic women with those in Hispanic women born in the United States.

"The San Francisco Bay Area has a very large Hispanic population, so it gave us a chance to study this population," Dr. John told Medscape Oncology. "We know from other studies that when women migrate from countries with a lower incidence of breast cancer, their risk of breast cancer tends to rise."

The increasing risk is dependent on a number of factors, explained Dr. John, "but in the case of Hispanics, the pattern suggests lifestyle factors may be the most prominent."

The longer women live in the United States, the more likely they are to adopt its lifestyle. "Women who immigrate at a young age have a higher risk than those who come at a later age," she said. "The most pronounced differences were seen between immigrants and third-generation [American]-born Hispanic women."

In this study, Dr. John and colleagues examined the risk-factor profile in 1024 American-born Hispanic women and 1509 foreign-born Hispanic women who participated in a population-based case–control study conducted in the San Francisco Bay Area. They identified 1253 cases of breast cancer through the Greater Bay Area Cancer Registry, and matched them with 1668 controls.

Overall, among the control group, women born in the United States tended to have a higher education, a family history of breast cancer, to have begun menstruating at a younger age, were more likely to use hormone replacement therapy, were taller, had a higher consumption of alcohol, and had a higher fat intake. All of these factors are associated with an increased risk for breast cancer, Dr. John pointed out.

Conversely, factors associated with a lower risk were more prevalent among foreign-born Hispanic women. They tended to have more children, breastfeed for longer periods of time, be more physically active, and consume more fiber. Over time, the researchers observed, Hispanic immigrants adopted behaviors that increased their risk for breast cancer while, at the same time, gave up protective behaviors. These changes in lifestyle were consistent with the observed increase in incidence.

"We definitely saw differences in diet, and that is something that changed significantly," said Dr. John. "It is a subject that we need more studies to focus on."

Dr. John also emphasized that there are some risk factors that cannot be changed. "We can't change family history," she said, "nor should we be advising women to have 5 children because it might lower their risk of breast cancer. Instead, we can advise them to be more active, eat a healthy diet, breastfeed, and maintain a healthy body weight as they move from a traditional lifestyle to a more Westernized one."

"These data are important," she added, "and will help us understand the breast cancer burden in Hispanic women. It is important to expand these studies to other Hispanic women to fully understand the problem of breast cancer in the full profile of Latina women."

American Association for Cancer Research Conference on the Science of Cancer Health Disparities: Abstracts PR-5 and A78. Presented February 4, 2009.

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