Women with few older female relatives may be unaware they carry a genetic risk of breast cancer, US researchers reported in a study that casts doubt on current genetic testing guidelines.
Genetic risk models for breast cancer underestimated a deadly gene mutation in women with fewer than two female relatives who lived to be older than age 45 on both sides of the family, according to researchers in California.
Both sides of the family are important because genetic breast cancer can be inherited from the father's lineage as well as the mother's, according to the study by the City of Hope cancer center published in the Journal of the American Medical Association. If the father has few or no sisters or aunts, the risk can go undetected.
Mutation of the tumor-suppressing BRCA gene boosts a woman's risk of breast cancer by 50 percent to 85 percent. Identifying women with this mutation who have already had breast cancer is important because their risk of recurrence is as high as 40 percent within 10 years without aggressive treatments.
The study included 306 women who had breast cancer before age 50 and no first- or second-degree relatives with breast or ovarian cancers. In about half of those cases -- 153 women -- there were few older females in the family.
The BRCA gene mutations were detected in 13.7 percent of those with few older female relatives compared to 5.2 percent among women with plenty of female relatives.