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Janet Gray, Ph.D.
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Immigrants, Migration Studies and Breast Cancer Worldwide

Researchers have long known that women who move from countries with lower breast cancer rates to industrialized countries soon acquire the higher risk of their new country, and this pattern has been one reason for enhanced attention to environmental links to breast cancer.

Worldwide, more than 1.38 million women were diagnosed with breast cancer in 2008 (Jemal, 2011). Almost 60 percent of total deaths from breast cancer occur in economically developing countries, even though the disease’s incidence rates (cases as a percent of population) and mortality rates (deaths as a percent of cases) are lower in these areas of the world (Jemal, 2011). This is due to the unequal population distribution across areas of the world with different economic resources.

The highest rates of breast cancer are found in the industrialized nations of North America and Western Europe. Intermediate incidence rates occur in South America and northern Africa, and the lowest incidence is generally found in western Asia and southern Africa. Even in these areas with lower rates, cancer of the breast is the most commonly diagnosed cancer in women (Parkin, 2006; Jemal, 2011).  

In northern Africa, as in many countries that are either developing or in transition, breast cancer rates are escalating sharply (Althius, 2005; Parkin, 2006; Jemal, 2011). While to some degree the highger rates may be associated with improved ability to detect the disease, changes in lifestyle and changes in reproductive patterns, migration studies suggest that much of the variation in international incidence rates might be environmentally related.  

Researchers have long known that women who move from countries with lower breast cancer rates to industrialized countries soon acquire the higher risk of their new country, and this pattern has been one reason for enhanced attention to environmental links to breast cancer.

Women who immigrate to the United States from Asian countries, where the rates are four to seven times lower, experience an 80 percent increase in risk after living in the United States a decade or more (Stanford, 2005; Ziegler, 1993). A generation later, the risk for their daughters approaches that of U.S.-born women. Hispanic women born in the United States have a significantly higher rate of breast cancer than do immigrant Hispanic women, but the longer the period of time immigrant Hispanic women spend in the United States, the greater their risk for breast cancer. This is especially true for women who immigrate before the age of 20 (John, 2005). Similarly, Swedish studies of people with many different cancers found that immigration at later ages meant an individual’s risk was more like that of the risk in their country of origin, while immigration early in life resulted in a level of risk more like that of the new country (Hemminki, 2002; Beiki, 2012).

There may be several explanations for the fact that immigration to industrialized countries increases risk of breast cancer, and these factors may interact with each other. Immigrants’ breast cancer risk — and that of their daughters — may increase if they adopt a Western lifestyle. Immigration may affect reproductive behavior, such as the use of oral contraceptives or choices about when and if a woman decides to have children. Immigration may also affect diet, including access to healthy foods, nutritional content, contaminants or food additives, or a combination of these factors. Immigration may also alter social and familial support, access to resources and health care, and may lead to increased social stress. In addition, moving to a more industrialized society may increase exposure to environmental pollutants that have been implicated in increased risk of breast cancer (Andreeva, 2007).