A new British report confirms that, although women with a close relative with breast cancer have an above-average risk of developing the disease, the risk is not as great as is often feared.
In fact, say the researchers at the Imperial Cancer Research Fund's Cancer Epidemiology Unit in Oxford, most women with a family history of breast cancer will never develop the disease. Similarly, most women who get breast cancer don't have a close relative with breast cancer.
The investigators analysed 52 studies with 58,209 women with breast cancer and 101,986 cancer-free women. They found that four out of five women who have a mother and a sister with breast cancer will never develop breast cancer, and 12 out of 13 will not die from the disease.
These data do indicate, however, that with a family history of breast cancer, the risk increases with the number of close relatives who have the disease.
For women with one close relative with breast cancer, the lifetime risk is 8 per cent. This increases to 13.3 per cent for those with two close relatives with the disease and to 21.1 per cent for those with three close relatives with breast cancer. Most women with affected relatives who get breast cancer themselves develop the disease at age 50 or later.
Nevertheless, eight out of nine women diagnosed with breast cancer - regardless of age - don't have an affected mother, sister or daughter (Lancet, 2001; 358: 1389-99).