Being Diagnosed at Younger Age Increases Risk of Cancer in Opposite Breast

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If you’ve been diagnosed with breast cancer, you’re 3 to 4 times more likely to develop a new cancer in the other breast (doctors call this contralateral breast cancer). This risk is different from the risk of the original breast cancer coming back. This risk also is higher than the risk of a first breast cancer in an average woman.

If you have an abnormal BRCA1 or BRCA2 gene and have been diagnosed with breast cancer, your risk of developing contralateral breast cancer ranges from 16% to 40% -- about 3 to 6 times higher than a woman who doesn’t have an abnormal BRCA1 or BRCA2 gene.

Doctors would like to have more precise estimates of contralateral breast cancer risk for diagnosed women with an abnormal BRCA1 or BRCA2 gene; this would help them develop screening and treatment plans tailored to a woman’s individual situation and personal contralateral breast cancer risk.

A Dutch study has found that women with an abnormal BRCA1 or BRCA2 gene who were diagnosed with a first breast cancer when they were younger than 41 had nearly double the contralateral breast cancer risk of similar women first diagnosed at age 41 to 49.

The study was published online on Dec. 23, 2015 by the Journal of Clinical Oncology. Read the abstract of “Impact of Age at Primary Breast Cancer on Contralateral Breast Cancer Risk in BRCA1/2 Mutation Carriers.”

People in the Netherlands have national health care, so researchers can review the records of every single woman who has been diagnosed with breast cancer.

For this study, the researchers identified 6,294 women who were diagnosed with invasive breast cancer at age 49 or younger. The women were treated between 1970 and 2003. The researchers tested tissue or blood samples from the women to see if they had an abnormal BRCA1 or BRCA2 gene:

  • 3.2% had an abnormal BRCA1 gene (200 women)
  • 1.1% had an abnormal BRCA2 gene (71 women)

The researchers didn’t say how many women had both abnormal genes.

After about 12.5 years of follow-up, 578 contralateral breast cancers were diagnosed in the women in the study:

  • 521 contralateral breast cancers were diagnosed in women with no known abnormal genes
  • 45 contralateral breast cancers were diagnosed in women with an abnormal BRCA1 gene
  • 12 contralateral breast cancers were diagnosed in women with an abnormal BRCA2 gene

The risk of being diagnosed with contralateral breast cancer 10 years after the first breast cancer diagnosis was:

  • 5.1% for women with no known abnormal genes
  • 21.1% for women with an abnormal BRCA1 gene
  • 10.8% for women with an abnormal BRCA2 gene

The difference in contralateral breast cancer risk between women with an abnormal BRCA1 or BRCA2 gene and women with no known abnormal genes was statistically significant. This means that it was likely because of the abnormal genes and not just because of chance.

The researchers then looked at contralateral breast cancer risk based on the age when a woman with an abnormal BRCA1 or BRCA2 gene was first diagnosed with breast cancer.

The risk of being diagnosed with contralateral breast cancer 10 years after the first breast cancer diagnosis was:

  • 23.9% for women first diagnosed when they were younger than 41
  • 12.6% for women first diagnosed at age 41 to 49

Being younger than 41 when first diagnosed didn’t increase the risk of contralateral breast cancer in women with no known abnormal genes.

If you’ve been diagnosed with breast cancer and know you have an abnormal BRCA1 or BRCA2 gene, you and your doctor will carefully consider your risk of developing a new cancer, as well as your preferences, as you develop your treatment plan. This study offers more information as you estimate your risk.

Depending on your risk, you may choose more aggressive steps to keep your risk as low as it can be, such as:

  • hormonal therapy to block the effect of estrogen on breast tissue or reduce the amount of estrogen in the body
  • removing the opposite breast and/or ovaries (prophylactic mastectomy and/or prophylactic oophorectomy)

There are also lifestyle choices you can make, such as avoiding alcohol and smoking, maintaining a healthy weight and exercising regularly.

Each woman’s situation is unique. Together, you and your doctor can estimate your risk and develop ways to manage it that are best for you.

For more information on steps you can take to reduce your risk of being diagnosed with a first or second breast cancer if you have an abnormal BRCA1 or BRCA2 gene, visit the Genetics page in the Breastcancer.org Lower Your Risk section.



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