Racial differences in the familial aggregation of breast cancer and other female cancers

Summary

Although breast cancer familial aggregation has been studied in Caucasians, information for African–Americans is scant. We used family cancer history from the Women’s Contraceptive and Reproductive Experiences study to assess the aggregation of breast and gynecological cancers in African–American and Caucasian families. Information was available on 41,825 first and second-degree relatives of Caucasian and 28,956 relatives of African–American participants. We used a cohort approach in which the relative’s cancer status was the outcome in unconditional logistic regression and adjusted for correlated data using generalized estimating equations. Race-specific models included a family history indicator, the relative’s age, and type. Relative risk (RR) estimates for breast cancer were highest for first-degree relatives, and the overall RR for breast cancer among case relatives was 1.96 (95% CI = 1.68–2.30) for Caucasian and 1.78 (95% CI = 1.41–2.25) for African–Americans. The effect of CARE participants’ reference age on their relatives’ breast cancer risk was greatest among first-degree relatives of African–American patients with RRs (95% CI) for ages <45 and ≥45 of 2.97 (1.86–4.74) and 1.48 (1.14–1.92), respectively. Among Caucasians, first-degree relatives of case subjects were at greater risk for ovarian cancer, particularly relatives younger than 45 years (RR (95% CI) = 2.06 (1.02–4.12)), whereas African–American first-degree relatives of case subjects were at increased cervical cancer risk (RR (95% CI) = 2.17 (1.22–3.85). In conclusion, these racially distinct aggregation patterns may reflect different modes of inheritance and/or environmental factors that impact cancer risk.