Even though researchers are beginning to understand the influence of genetic factors on the incidence of breast cancer in largely white, Western populations of women, very little is known about breast cancer risk attributable to inherited factors in other populations. The few studies that have examined breast cancer risk in African-American women have concluded that a family history of breast cancer confers a magnitude of increased risk similar to that seen in white population–based studies.
Few African-American families in whom breast cancer fits an autosomal dominant pattern of inheritance have been described in the literature. This lack could reflect a low prevalence of breast cancer–related inherited mutations in African-Americans, but it is equally likely to be due to selection or referral biases. In fact, some of these families are now known to carry BRCA1 or BRCA2 mutations, but a cohort ascertained for the purpose of estimating population frequencies has not been assembled.
Only one study of familial breast cancer clustering in North American Hispanic individuals has been conducted. This study of Hispanic women living in Laredo, Texas, from 1870 to 1981 suggested that familial clustering of breast cancer also appears in this population. However, the study design allowed for a significant margin of error, predominantly from underreporting of cases.
No epidemiologic information from outside the United States is available on Hispanic populations; however, estimates are available from Spain on BRCA1 and BRCA2 mutation prevalence in a breast cancer population. These data suggest that the incidence of BRCA1 mutations is similar to that seen in other European populations. Thus, breast cancer susceptibility gene mutations may be equally prevalent throughout South America, as Spain provided many of the founders of the white population on that continent.
One study of family history of breast cancer in Japanese women living in Japan has been reported in the English medical literature. In this study, the relative risk of developing breast cancer of women with two or more affected relatives was 2, comparable to that in studies involving primarily white women. Reports of BRCA1 germ-line mutations in Japan suggest that the prevalence of BRCA1 mutations may be lower than in Western countries, but BRCA2 mutation rates may be similar to those seen in Western populations.
Finally, a study of breast cancer in Arab women included 73 breast cancer cases identified at a single hospital in Israel and found 15 patients (20%) who reported at least one affected family member. This study again suggests that breast cancer risk attributable to inherited susceptibility genes of high or moderate penetrance may be relatively uniform throughout the world; yet, once again, the work needed to genetically characterize these populations has not been done.
Angela DeMichele and Barbara L. Weber
A. DeMichele: Departments of Medicine and Epidemiology, The University of Pennsylvania Cancer Center, Philadelphia, Pennsylvania
B. L. Weber: Departments of Medicine and Genetics, Breast Cancer Program, Population Science and Cancer Control, The University of Pennsylvania Cancer Center, Philadelphia, Pennsylvania