"Women who have a sister diagnosed with breast cancer remain at increased risk of breast cancer throughout their lives, epidemiologists in Sweden report in the
Journal of the National Cancer Institute for May 21.
"The contributions to familial breast cancer risk of the age of the 'at-risk' woman, the age at diagnosis of the first case in her family, and the time since the index diagnosis 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 in order to guide screening strategies for at-risk women.
By linking data from Statistics Sweden's "Multi-Generation Register" with the Swedish Cancer Register, Dr. Reilly's group identified 16,505 index cases of breast cancer who had 23,654 sisters with follow-up time after the diagnosis of the index sister; 714 of the sisters developed breast cancer.
Compared with the general population, the risk of breast cancer in sisters of affected women was highest among those in their 20s and 30s; the incidence rate ratio was 6.64, which declined to about two after age 50.
The risk was relatively independent of the age of the index case at 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 index 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," Dr. Reilly and her colleagues advise."
