A large new study has reported that women who have a first-degree relative (mother, sister or daughter) with breast cancer have a 73% higher risk of triple negative (ER-/PR-/HER2-) breast cancer than women without familial breast cancer. However, such women also have a 62% higher risk of estrogen receptor positive (ER+) breast cancer, which is the most common type, and a 56% higher risk of hormone receptor negative/HER2 overexpressing breast cancer (ER-/PR-/HER2+).

Triple negative breast cancer accounts for fewer than 20% of breast cancers overall, but it is the predominant subtype among BRCA1 mutation carriers. However, few studies have examined the association between family history of breast cancer and risk of triple negative breast cancer. The authors examined data from 2,599,946 mammograms on 1,054,466 women aged 40 to 84 years collected by the Breast Cancer Surveillance Consortium. Fifteen percent of these women reported a first-degree family history of breast cancer .

A total of 705 women were found to have triple negative disease, 10,026 had ER+ disease, and 308 had ER-/PR-/HER2+ breast cancer. First-degree family history was found to similarly increase the risk of all three subtypes. Risk was highest among women with at least two first-degree relatives with breast cancer. Compared to women with no affected first-degree relatives, those with at least two affected first-degree relatives had 2.66 times the risk of triple negative breast cancer, 2.05 times the risk of ER+ breast cancer, and 2.25 times the risk of ER-/PR-/HER2+ breast cancer.