Risk factors for breast cancer in a black population: The Barbados National Cancer Study

A21

Whereas overall incidence of breast cancer (BC) is lower in African American (AA) women than in white women, incidence tends to be higher in younger AA women and their overall mortality is also higher. To determine reasons for these cancer patterns in AA, it is useful to study populations across the African diaspora, such as African-Caribbeans. This report presents the first nationwide epidemiologic data on BC risk factors in an African-Caribbean population. Results are based on the Barbados National Cancer Study (BNCS), a population-based case-control study to investigate epidemiologic and genetic factors for breast and prostate cancer in Barbados, West Indies. Barbados. has a predominately African-descent population, with the same ancestral origin as AA. African Barbadians (AB) represent an important intermediate group for comparisons of populations across the African diaspora.. In fact, the age-standardized BC incidence in Barbados is approximately midway between the rates noted for West Africa and AA, with similarly high mortality as that of AA.
 The study included 241 histologically-confirmed incident cases (80% participation), identified by the country’s only Pathology Department between July 2002 and March 2006, and 481 age-matched female controls (82% participation), randomly selected from a national database and frequency matched (2 to 1) to the cases by 5-year age groups. Multivariable logistic regression analyses were used to evaluate potential associations, presented as odds ratios (OR) and 95% confidence intervals (CI).
 The mean ages of cases and controls were 57 and 56 years, respectively. Approximately 94% of BNCS participants self-reported their ancestry as black or mixed (black and white). Among these AB participants, significant risk factors included older age at first-term pregnancy (OR (95% CI):1.04 (1.00, 1.07) per year) and a history of benign breast disease (1.9 (1.2, 3.1)). Increased parity was negatively associated with BC, with ORs decreasing from 0.4 (0.2, 0.9) in those having 1-2 children to 0.3 (0.1, 0.7) among those having 3+ children, as compared to nulliparous women, with the protective effect mainly seen in post-menopausal women. Furthermore, over 20% of cases and only 8% of controls reported a family history of BC, resulting in an OR of 2.6 (1.6, 4.4) for any self-reported family history of BC; 3.8 (1.4, 10.3) for reported history in mother and 3.1 (1.4, 7.0) in sisters.
 Reproductive patterns of AB women were more similar (or intermediate) to those reported for West African (WAfr) women than for AA women. The AB and WAfr women had a later age at menarche (13 years for AB, 15 years for WAfr, 12 years for AA), a higher rate of lactation, and less frequent use of exogenous hormones than AA women. On the other hand, AB and AA share many westernized lifestyle factors compared to WAfr women. Barbados thus represents an intermediate population in the diaspora, which may in part explain why the incidence in AB women is lower than in AA but higher than in WAfr women.
 BC is a multifactorial disease that is likely the result of interacting genetic and environmental factors. Molecular genetic analyses in BNCS, which are ongoing, may identify common variants that may be particularly important in the development of BC in this and other populations of African origin.
 The BNCS was funded by the National Human Genome Research Institute.