NEW YORK (Reuters Health) - Women who have a sister diagnosed with breast cancer have a higher than average risk of also developing the disease, and this increased risk will persist for the rest of their lives, epidemiologists in Sweden report in the Journal of the National Cancer Institute.
The contribution to breast cancer risk of factors, such as age of the "at-risk" women; age of the sister at the time of diagnosis; and the time elapsed since the diagnosis was made, is unclear, Dr. Marie Reilly and colleagues at the Karolinska Institute in Stockholm note. Their goal was to determine relative risk associated with these factors to help guide screening strategies for at-risk women.
By linking data from Sweden's "Multi-Generation Register" with the Swedish Cancer Register, Reilly's group identified 16,505 women with breast cancer and 23,654 of their sisters; 714 of the sisters developed breast cancer. The data were collected for the years 1958 through 2001.
Compared with the general population, the risk of breast cancer in the sisters of affected women was highest among those in their 20s and 30s. Overall the risk of cancer was increased by about 6.64-fold, but declined to about 2-fold after age 50.
The risk was relatively independent of the age of the first woman in the family with a diagnosis, the authors note, suggesting that "there is not a predetermined age at which members of a family enter a high-risk state."
Overall, the risk of breast cancer in women with sisters with breast cancer was double that of other women for at least 20 years after the sister's diagnosis.
"This suggests a need for intensive screening of sisters in affected families for the rest of their life, independent of the age-related screening recommendations," Reilly and her colleagues advise.
SOURCE: Journal of the National Cancer Institute, May 2009.
