Family History of Breast Cancer Dramatically Increases Risk of Cancer in Other Breast

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Women with close relatives who've been diagnosed with breast cancer have a higher risk of developing the disease.

If you've had one first-degree female relative (sister, mother, daughter) diagnosed with breast cancer, your risk is doubled. If two first-degree relatives have been diagnosed, your risk is 5 times higher than average.

If your brother or father have been diagnosed with breast cancer, your risk is higher, though researchers aren't sure how much higher.

Women who have been diagnosed with breast cancer have a higher risk of both a second primary breast cancer in the same breast, as well as being diagnosed with breast cancer in the opposite breast, called contralateral breast cancer.

Small studies have suggested a link between a family history of breast cancer and a higher risk of contralateral breast cancer in women who have been diagnosed.

A large study now adds more evidence that a family history of breast cancer dramatically increases the risk of contralateral breast cancer in young women, even among women who don’t have a genetic mutation linked to breast cancer.

The research was published online on April 5, 2018 by the Journal of Clinical Oncology. Read the abstract of “Breast Cancer Family History and Contralateral Breast Cancer Risk in Young Women: An Update From the Women’s Environmental Cancer and Radiation Epidemiology Study.”

In the second phase of the Women’s Environmental Cancer and Radiation Epidemiology (WECARE) study, the researchers used cancer registry records to identify 1,521 women younger than 55 who were diagnosed with a first invasive breast cancer in one breast between 1985 and 2008 and had contralateral breast cancer diagnosed at least 2 years after the first diagnosis. The researchers matched these women, considered the cases, to 2,212 women who had been diagnosed during the same time period with cancer in only one breast, considered the controls, on the basis of:

  • age at diagnosis
  • year of diagnosis
  • ethnicity
  • cancer registry region

All the women were from the United States, Canada, and Denmark.

The researchers asked all the women about any breast cancer risk factors that may apply to them, including taking a detailed family history, smoking, alcohol use, and childbearing history.

A subset of the women was tested for the following mutations linked to higher breast cancer risk:

  • BRCA1
  • BRCA2
  • ATM
  • CHEK2
  • PALB2

Among the women who had genetic testing, 130 (18%) women diagnosed with contralateral breast cancer and 93 (7%) women diagnosed with cancer in only one breast had at least one mutation linked to higher breast cancer risk.

Using statistical analysis tools, the researchers found that women who had a first-degree relative that had been diagnosed with breast cancer had nearly twice the risk of contralateral breast cancer when compared to women with no family history of the disease.

Women who had a second-degree relative (cousin, aunt) diagnosed with breast cancer had a 40% higher risk of contralateral breast cancer compared to women with no family history of the disease.

Contralateral breast cancer risk was highest in women who had a first-degree relative who had been diagnosed with breast cancer in both breasts.

The link between family history and contralateral breast cancer risk was affected by the age at which the relative was diagnosed. When a woman’s first-degree relative was younger than 40 at diagnosis, the woman’s risk of contralateral breast cancer was more than 3 times higher compared to women with no family history of the disease.

For women who had a first-degree relative younger than 40 when diagnosed with cancer in both breasts, the risk of contralateral breast cancer was more than 10 times higher compared to women with no family history of the disease.

When the researchers looked only at women who had tested negative for any of the mutations linked to a higher risk of breast cancer, the results were similar: women who had a first-degree relative diagnosed with breast cancer had nearly double the risk of contralateral breast cancer compared to women with no family history of the disease.

“Family history of breast cancer remains a strong risk factor for contralateral breast cancer, even after excluding carrier of deleterious mutations,” the researchers wrote. “Family history of breast cancer is relatively easy to assess accurately and even in the absence of genetic testing can inform the assessment of contralateral breast cancer risk and influence first primary breast cancer treatment decisions, such as prophylactic surgery or systemic therapy.”

While you can’t change your family history, it makes sense to keep your knowledge of it as updated as possible. If you’ve been diagnosed with breast cancer, tell your oncologist about any cases of cancer in your family that you know about -- in both women and men -- even cancers that aren’t breast or ovarian. Your family history can help you and your doctor accurately assess your contralateral breast cancer risk and decide if a more aggressive treatment plan, such as removing the other healthy breast, is right for your unique situation.

For more information on breast cancer risk and steps you can take to reduce your risk of recurrence/contralateral breast cancer, visit the Breastcancer.org Breast Cancer Risk Factors pages.


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