Women with a family history of breast cancer have a higher risk of breast cancer and are more likely to get breast cancer at a younger age than those without such as history. The degree of extra risk varies according to whether breast cancer was diagnosed among first degree relatives (parent, sibling or child), second degree relatives (e.g., grandparent, aunt/uncle, half-sibling), or multiple family members. Breast cancer risk is also inherited from the father's side of the family. Familial breast cancer tends to be more aggressive than nonfamilial breast cancer. Prognosis also appears to be partly heritable — women whose mothers died of breast cancer are also more likely to die from it, even adjusting for tumor characteristics.
The majority of women with a family history of breast cancer are not BRCA mutation carriers. However, most studies of familial breast cancer incorporate BRCA mutation carriers because they could not be excluded from the data. Please see our article on BRCA1 and BRCA2 mutation carriers for information specific to such carriers.
Mother with breast cancer
The risk of breast cancer and likely age at diagnosis for daughters of women with breast cancer depends on the mother's age at diagnosis. Daughters of mothers with premenopausal breast cancer have a higher risk of breast cancer than those of mothers with postmenopausal breast cancer. One 2012 study of nurses health study participants reported that daughters of mothers who were diagnosed before age 50 had approximately 1.7 times the risk of breast cancer as women without a family history of breast cancer. On the other hand, daughters of mothers who were diagnosed at 50 or older had approximately 1.4 times the risk as those without a family history.
The risk for relatives of women with very early-onset breast cancer are considerably higher. One Australian study found that parents and siblings of women without BRCA mutations who were diagnosed before age 35 had four times the risk of breast cancer as expected.
Subsequent generations of women with familial breast cancer tend to be diagnosed with breast cancer at younger ages. A Swedish study reported that the age to reach the same cumulative incidence of breast cancer as women without family history was lower, especially when the older relative was diagnosed at a relatively young age. For example, daughters of mothers who were diagnosed with breast cancer before age 40 were found to reach the level of risk that women lacking a family history had at the age of 50 approximately 12.3 years earlier. On the other hand, daughters of mothers who were diagnosed at age 82 and older reached the level of risk of women aged 50 without a family history approximately 3.3 years earlier.
Sister with breast cancer
Having a sister with breast cancer confers a similar or slightly higher risk of breast cancer as having a mother with breast cancer. Sisters of women who were diagnosed before age 50 had approximately 1.7 times the risk of breast cancer as women without a family history of breast cancer among nurses health study participants. On the other hand, sisters of women who were diagnosed at 50 or older had approximately 1.5 times the risk as those without a family history.
A 2015 Scandinavian study reported that twin sisters of women diagnosed with breast cancer had approximate 3.5 times the risk of breast cancer as the general population if they were identical twins and 2.5 times the risk if they were fraternal twins.
Grandmother or other second-degree relative with breast cancer
Little data is available with respect to the extra risk conferred by having a second-degree relative (grandparent, grandchild, aunt/uncle, niece/nephew, or half-sibling) with breast cancer. One Swedish study reported that having a grandmother with breast cancer was associated with similar excess breast cancer risk (1.27 times the normal risk) as having an affected half sister (1.26) for maternal relatives. The risk was found to be higher when relatives on the father's side had breast cancer (1.39 times the normal risk when the paternal grandmother had breast cancer and 1.50 times when a half sister was affected).
Father or brother with breast cancer
Having a father with breast cancer increases breast cancer risk among daughters similarly to having a mother with breast cancer. However, having a brother with breast cancer increases breast cancer risk compared to having a sister with breast cancer. The Swedish study mentioned above found that the relative risk for a woman increased 2.48 times when a brother had breast cancer compared to 1.87 when a sister was affected. Male breast cancer appears to have a stronger genetic basis than female breast cancer.
Multiple family members with breast cancer
Having more than one first- or second-degree relative with breast cancer increases breast cancer risk more than having one such relative. Having at least two female first-degree relatives with breast cancer increases the relative risk at least to 2.8 times the normal risk, according to the Swedish study above. When both parents are diagnosed with breast cancer, the risk for their daughters is increased tenfold.
Family history and breast cancer type
While women with a family history of breast cancer are at higher risk for all types of breast cancer, the excess risk is heightened for triple negative breast cancer. Triple negative breast cancer is a subtype of breast cancer that is estrogen receptor negative (ER-), progesterone receptor negative (PR-), and human epidermal growth factor receptor 2 negative (HER2-). Triple negative breast cancer accounts for fewer than 20% of breast cancers overall. However, one study reported that women with a first-degree family history of breast cancer had similar risks of triple negative breast, ER-/PR-/HER2+ (another aggressive subtype) and ER+ breast cancer (the most common type). In other words, a first-degree family history of breast cancer was associated with increased risk of aggressive breast cancer.
Women with lobular breast cancer are more likely to have a father diagnosed with cancer than women with ductal breast cancer. The most frequent cancer diagnosis among the fathers is prostate cancer but the association between lobular breast cancer and a father with cancer remained significant even after excluding prostate cancer in one study. In fact, in comparison with the other breast cancer types, sarcoma and leukemia occurred more often in fathers of lobular breast cancer patients.
Influence of having a family history of breast cancer on prognosis
Breast cancer prognosis runs in families. In other words, there are similarities in survival among first-degree relatives. A Swiss study categorized women into poor, medium, or good survival risk groups according to breast cancer-specific survival of their mothers or sisters. Women in the poor familial survival risk group were almost five times more likely to die of breast cancer than those in the good survival risk group, even after adjusting for patient and tumor characteristics and type of treatment.
A Swedish study reported that the risk of breast cancer was somewhat higher for those whose mothers died of it compared to those with a nonfatal family history. In fact, 51.0% of the women with familial breast cancer had a fatal family history. Risk of death in daughters of mothers who died from breast cancer was almost twice as high as that of daughters of mothers who had breast cancer but did not die of it. The majority of daughters with a fatal family history were diagnosed after their mothers' deaths. Tumor stage classification did not appear to vary according to fatal or non-fatal family history.
Screening for familial breast cancer
Very high risk women are normally advised to begin annual screening for breast cancer at age 25. This guideline makes sense in that it is likely to provide cancer-free baseline images to which subsequent imaging results can be compared. Of course, high-risk women with symptoms of breast cancer should be screened as soon as any symptoms are detected (although very rare, even teenagers can develop breast cancer).
However, not all women with a family history are considered very high risk. Risk also increases over time, depending on when other family members were diagnosed. Women whose mothers develop breast cancer in their thirties appear to be at risk of being diagnosed with breast cancer as much as 12 years earlier. For example, if a mother was 37 at diagnosis, her daughter's risk might increase sharply starting at age 25. Those whose mothers were in their forties at diagnosis appear to be at heightened risk of being diagnosed starting 10 years earlier. Those whose mothers were in their fifties at diagnosis appear to be at heightened risk of being diagnosed starting eight years earlier. Obviously, these are not hard and fast numbers, just an attempt to provide some guidelines using the limited available data. Note that a large minority of even the highest risk women never develop breast cancer.
Please see our article on how to protect our daughters from breast cancer for steps that can be taken to reduce the risk of breast cancer in our high risk daughters. Below are links to recent studies on this topic. For a more complete list of studies, please click on family history.