Women who have close relatives with breast cancer but who test negative for key genetic mutations associated with the disease are still at increased risk of developing breast cancer, researchers report.

The study found that even if tests fail to detect the breast cancer-linked BRCA1 and BRCA2 gene mutations in these women, they are still about three times more likely to develop breast cancer by age 50 than women in the general population.

These women should be regularly screened for breast cancer starting at ages 35 to 40, advised researchers at St. Mary's Hospital in Manchester, United Kingdom.

They assessed the families of 277 women with faults in the BRCA1 and BRCA2 genes. Of those 277 women, 190 had breast cancer, 48 had ovarian cancer, and 33 had both types of cancer. Six of the women were cancer-free.

Of the women's 531 female relatives tested for faults in the BRCA1 and BRCA2 genes, 49 percent tested negative. Of those who tested negative, 28 developed breast cancer and four developed ovarian cancer.

Faults in the BRCA1 and BRCA2 genes account for about 5 percent of all diagnosed breast cancer cases in developed countries. However, faults in these genes greatly increase a woman's risk of developing early breast and/or ovarian cancer compared with women in the general population.

The findings were published in the November issue of the Journal of Medical Genetics.