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A study recently published in The Lancet demonstrated that although women who have first-degree relatives with a history of breast cancer are at increased risk for the disease, most will never develop breast cancer and those who do will likely be over 50 years old when diagnosis occurs. In addition, eight out of nine women who develop breast cancer do not have an affected mother, sister, or daughter.

Previous studies have suggested that a woman’s risk of developing breast cancer increases if she has a family history of the disease. However, no study has been large enough to characterize this risk reliably. This report combined data from 52 epidemiological studies to investigate the influence of breast cancer on first-degree relatives (mothers, sisters, and daughters).

Individual data from 58,209 women with breast cancer and 101,986 women without breast cancer were collected, verified, and reanalyzed by the Collaborative Group on Hormonal Factors in Breast Cancer. The overall analysis indicated that 87% of women with breast cancer did not have any affected first-degree relatives, while 12% of the women reported one affected relative, and only 1% had two or more affected relatives. Eight out of nine women with breast cancer do not have any affected first-degree relatives.

The likelihood of a cancer diagnosis did increase as the number of affected relatives increased. For women in more developed countries, the estimated incidence of breast cancer up to age 50 was 1.7%, 3.7%, and 8.0% respectively for zero, one, and two affected first-degree relatives. The estimated incidence of breast cancer up to age 80 was 7.8%, 13.3%, and 21.1% respectively for women with zero, one, and two affected first-degree relatives. These results demonstrate an increased risk, but also suggest that a woman with affected relatives will rarely develop breast cancer herself. For example, four out of five women in more developed countries with two affected first-degree relatives would never be diagnosed with breast cancer.

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The incidence of death due to breast cancer up to age 80 was 2.8%, 4.2%, and 7.6% respectively for women with zero, one, and two affected first-degree relatives. Analysis indicated that one in 13 women with two affected first-degree relatives would die from the disease. These data suggest that even women with a history of familial breast cancer who are diagnosed themselves are not likely to die from the cancer.

Other factors, such as menopausal status, number of sisters, and childbearing history did not significantly alter the risk associated with familial history of breast cancer. There was also no substantial difference in breast cancer between women with affected mothers or sisters. The data did suggest that women with a family history of breast cancer who do develop the disease will most likely be diagnosed in middle or old age, and indicated that the age at which first-degree relatives received a cancer diagnosis has only a moderate effect on lifetime risk for developing breast cancer.

These results have important implications on screening programs for breast cancer. Because most women with one or more affected first-degree relatives are unlikely to develop breast cancer themselves and few women who do develop breast cancer have a mother, sister, or daughter with a history of the disease, public health programs should not focus solely on early detection of breast cancer in women with a familial history of the disease. Such programs would fail to diagnose a majority of women who develop breast cancer. (Lancet, Vol 358:1389-99, 2001)

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