How Family History Effects the Probability of BRCA1 or BRCA2

Jill E. Stopfer
Last Modified: November 1, 2001

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Question
Dear OncoLink "Ask the Experts,"
I am wondering what the probability is of finding the gene alterations BRCA1 or BRCA2 in a family where:

  • only one person in the family is affected by breast cancer or ovarian cancer;
  • two persons in the family are affected by breast cancer or ovarian cancer;
  • only one person in the family is affected both with breast cancer and ovarian cancer?
Also, what is the risk for breast and ovarian cancer in the people you find to be BRCA1 and/or BRCA2 mutation carriers?


Answer
Jill E. Stopfer, MS Certified Genetic Counselor for the University of Pennsylvania Cancer Risk Evaluation Programs, responds:

There are several issues in calculating the chance of finding a BRCA1 or BRCA2 alteration, also called the "prior probability" of finding a mutation. The only way to determine the prior probability is to take a detailed family history. The family history must include all cancer diagnoses, not just breast and/or ovarian cancer, all ages at diagnosis, and ethnicity. An individualized risk assessment would shed more light on your personal risk. Also, please speak to your doctor about the appropriate screening guidelines for a person with your profile and family history. If you are interested in finding a cancer genetics professional in their area—there is a site within the NCI that can provide that information. Please see The Familial Cancer Risk Counseling & Genetic Testing Information Search Form

The cancer risks associated with a BRCA1 or 2 mutation are usually presented as a range, since different studies have come up with different risk information.

LIFETIME breast and ovarian Cancer risks for BRCA1:

  • breast (female) 56-85%
  • ovarian 20-60%
  • other associated cancers, risks less clearly defined: prostate, colon
LIFETIME breast and ovarian cancer risks for BRCA2:
  • breast (female) 56-85%
  • ovarian 10-20%
  • breast (MALE) 6%
  • other associated cancer, risks less clearly defined: prostate, pancreatic



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