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The results of pooling information from 52 epidemiological studies on 58,209 women with breast cancer and 101,986 unaffected controls provide the most reliable estimates available so far for the breast cancer risk associated with a family history of the disease (assessed only as the number of affected first degree relatives) [Collaborative Group on Hormonal Factors in Breast Cancer (2001) Lancet 358, 1389-1399]. Overall, the relative risk of breast cancer was calculated to be 1.80, 2.93 and 3.90 for women with one, two, or three or more affected first degree relatives. The cumulative incidence of breast cancer for women aged 20 to 80 was 7.8%, 13.3% and 21.1% for women with zero, one and two affected first-degree relatives, and the corresponding cumulative risk of death from breast cancer was 2.3%, 4.2% and 7.6%. For women with at least one first-degree relative with breast cancer, the age at which that relative was diagnosed did affect risk, but only slightly. Factors other than family history, such as parity and oral contraceptive use had no consistent affect on the risk associated with family history. Overall, 87% of women with breast cancer had no affected first degree relative.

Comment: The authors comment that, in public health terms, there is not much to be gained by, for example, concentrating breast cancer screening on women with a family history of the disease, as even if screening were completely effective, such a strategy could only have a very small impact on the overall incidence of disease in the population. They also point out that, although a 21% cumulative risk of breast cancer seems high for women with two affected first degree relatives, it still means that nearly 80% of such women will never contract breast cancer and still fewer would die of this disease. This analysis is reassuring, but it is still clear that women in families with multiple affected relatives, especially where disease occurs at a young age, are at substantially increased risk, and that additional screening or preventive strategies in this very small percentage of families are justified.