Family history is a significant risk factor for breast cancer, especially in women who have first-degree relatives with the disease. That risk might be even higher if there is a first-degree relative with prostate cancer, a new study suggests.
In women with a family history of prostate cancer, there was a 14% increase in the relative risk of developing breast cancer. However, in women with a family history of both breast and prostate cancer, the relative risk increased to 78%.
In addition, the risks associated with a family history of both breast and prostate cancer was higher in black women than in white women.
The study was published online March 9 in Cancer.
"While this study is limited to largely postmenopausal women, one might expect to see a similar or stronger risk in younger women," said first author Jennifer Beebe-Dimmer, MPH, PhD, from the Karmanos Cancer Institute and Wayne State University School of Medicine in Detroit.
"We tend to see a stronger family history of breast cancer among women diagnosed at younger ages, and the same may be true for a family history of prostate cancer," Dr Beebe-Dimmer told Medscape Medical News.
"We believe that physicians may want to consider family history of prostate cancer in addition to breast cancer before making recommendations about screening," she added.
Dr Beebe-Dimmer pointed out that there is some evidence that men might have a higher risk for prostate cancer if they have first-degree relatives with breast cancer.
"We and others have shown the opposite association, particularly when female relatives are diagnosed with early-onset disease," she said. "It has been suggested that a relatively small proportion of the prostate cancer cases diagnosed in families with breast and/or ovarian cancer are related to BRCA1/2, suggesting that there may be other genes and/or shared environmental exposures that explain the clustering."
Multiple Relatives Increases Risk
Dr Beebe-Dimmer and her colleagues evaluated 78,171 women who participated in the Women's Health Initiative Observational Study from 1993 to 1998. The women were followed for a median of 132 months from the date of enrollment, and there was a median of 60 months between enrollment and the diagnosis of breast cancer.
There were 3506 cases of incident breast cancer diagnosed in the cohort up to August 31, 2009.
Participants with breast cancer were more likely than those without to be white non-Hispanic and college educated, and to have a history of hormone use and benign breast disease. They were also more likely to have undergone mammography screening within 2 years of the baseline examination.
Median age at the time of breast cancer diagnosis was 69 years (range, 50 - 90 years).
A positive family history of breast cancer was reported by 11,608 women in the cohort, and women with breast cancer were more likely than those without to report a family history of the disease (20.5% vs 14.6%).
Having a single family member with breast cancer was associated with an increase in risk of approximately 40%, after adjustment for cofounders (hazard ratio [HR], 1.42; 95% CI, 1.30 - 1.55). Having multiple family members with breast cancer increased that risk (adjusted HR [aHR], 1.66; 95% confidence interval [CI], 1.32 - 1.88).
Women with breast cancer were also more likely than those without to report that at least one first-degree relative had been diagnosed with prostate cancer (11.6% vs 10.1%). This family history was associated with a significant, albeit modest, increase in breast cancer risk after adjustment for confounders such as a family history of breast cancer (aHR, 1.14; 95% CI, 1.02 - 1.26).
The risk was highest for those with a family history of both breast and prostate cancer (aHR, 1.78; 95% CI, 1.45 - 2.19).
When the data were stratified by race, the risk was highest in black women who had "multiple affected first-degree family members" (aHR, 2.85; 95% CI, 1.33 - 2.08).
A family history of prostate cancer was modestly predictive in both white and black women, but only reached statistical significance in white women. Although black women with a family history of both diseases appeared to be at greater risk of developing breast cancer (aHR, 2.34; 95% CI, 1.09 - 5.02), "the risk estimates were not significantly different as evidenced by the overlapping CIs," note Dr Beebe-Dimmer and colleagues.
The Women's Health Initiative (WHI) is funded by the National Heart, Lung, and Blood Institute. Dr Beebe-Dimmer and some of her coauthors report receiving funding as independent contractors from the WHI Midwest Regional Center.
Cancer. Published online March 9, 2015. Abstract
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