Risk with Negative Genetic Testing
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.