Last Modified: January 27, 2009
Dear OncoLink "Ask The Experts,"
My sister was diagnosed with DCIS and had mastectomy. My Mom was just diagnosed as well. My sister tested negative in the genetic testing to see if she carried the gene that would affect her daughters. Does that mean they can never get breast cancer? My sister said they are cleared, but I am not because of my Mom. Please clarify.
Jill Stopfer, MS, CGC, Certified Genetic Counselor, responds:
This is a common misconception and underscores the importance of genetic counseling by a qualified professional so people don't just have genetic testing, but understand the results, and the meaning of these results regarding their risk and follow-up recommendations.
First of all, there is a common misconception that there is one "breast cancer gene" that accounts for all inherited risk for breast cancer, or for the breast cancer that runs in families. This is not the case. There are many, many genes that may influence one’s chances of developing breast cancer. Only some of the genes have been identified so far, and only a few of them are available now for clinical (commercial) testing. The best known of these breast cancer genes are BRCA1 and BRCA2. If there is a family history of breast cancer that looks suspicious, meaning it looks to have a familial component, these two genes will be responsible only 50% of the time. This means that you can have familial, or hereditary risk for breast cancer, but have it due to something other than BRCA1/2. It's possible that a different gene, or set of genes, could underlie familial risk in the
family asking the question below. When an individual is tested and found to be negative for BRCA1/2, then the history is still unexplained, and may or may not be due to significant genetic or inherited factors.
Bottom line, risk assessment and counseling is just as important as the blood test! The daughters of this woman who tested negative may still be at increased risk. It would be inappropriate for this next generation to assume that they are at average risk just because their mother was tested and was negative for two of many possible genes that could increase breast cancer risk. In addition, there is no woman who has a zero risk for developing breast cancer, since most breast cancer cases have nothing to do with BRCA1/2. The sister is at increased risk with a mother and sister with breast cancer, and may benefit from enhanced surveillance, as will the next generation when they are older (since no ages are given I cannot say when screening should begin, but this would be discussed in a session with a genetic counselor).