Background: The excess risk of breast cancer among Jewish women has been attributed to the effects of difference in lifestyle and reproductive patterns, but there is now evidence that Jewish women may be more likely than other women to inherit mutations in breast-cancer genes. We investigated whether any excessive risk among Jewish women is confined to those with a family history of breast cancer.
Methods: We assessed the effect of Jewish religion on breast cancer in a large population-based case-control study (6611 women with breast cancer and 9026 controls) in USA. Participants were given telephone interviews and asked about known and suspected risk factors for breast cancer.
Findings: Overall, Jewish women had only a slightly raised relative risk of breast cancer (1.10 [95% CI 0.84-1.44]; p=0.49). However, the relative risk was much higher for Jewish women with a first-degree relative who had breast cancer (3.78 [1.74-8.16]; p<0.001). The effect of family history was greater in Jewish women than in women of other religions (p interaction = 0.05).
Interpretation: These results are consistent with data suggesting that certain groups of Jewish women have a higher than expected rate of mutation in the breast-cancer gene BRCA1.