September 03, 2010
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Genetic Counseling and Breast CancerDr. Dharmen Patel was most recently Fellow at Westchester Medical Center and Dr. Lawrence Shapiro is Professor of Pediatrics at New York Medical College and Director, Regional Medical Genetics Center, Westchester Medical Center.
Not long ago, breast cancer was shrouded in mystery. Though doctors knew it affected the human body and had a number of fairly effective treatments, they knew little about its cause. The same could be said for the factors that affect risk. Now, however, thanks to recent advances in genetics, this is all changing, and quickly. Today medical scientists can pinpoint mutations in individual genes which increase breast cancer risk. While these mutations do not account for all cases of breast cancer — there are other factors remaining to be explored — the presence of the mutations offers a more accurate picture of a person's risk for breast cancer. Some of these mutations are passed down through families and ethnic groups. For many women, this has important implications for monitoring, prevention and even treatment of breast and other cancers, such as ovarian cancer. For example, let us look at the case of one real woman. The Case of "Sarah"
A 44-year-old woman, whom we will call Sarah, is asking her doctor for advice about whether or not to seek genetic counseling. With good reason — she has an extensive family history of breast and ovarian cancer. Her mother had been diagnosed with ovarian cancer at age 67. Her maternal grandmother reportedly had breast cancer in her 40's. Her maternal aunt had breast cancer in her 30's. Recently, this aunt had genetic testing and was found to carry a gene mutation known to be associated with breast cancer.
Sarah's family is of Ashkenazi (Eastern or Central European) Jewish ancestry. She is premenopausal and has never taken oral contraceptives. She exercises one half-hour a day, three days a week. She does not smoke or drink. She has three children, a daughter who is 21 years old and two boys, 23 and 17. Her physical examination is normal, as was a mammogram done the year before. A Question of Risk
What did Sarah's doctor tell her? According to what we know today, there are two categories of risk faced by women like Sarah. One relates to the gene mutation she shares with her aunt; this carries a definite and quantifiable risk for breast cancer. The other type of risk faced by Sarah is 'familial tendency' — Sarah is at greater risk of developing breast cancer simply because of her family history, whether or not her tests turn up a known gene mutation.
The risk from familial tendency can be expressed in this way: first degree relatives of breast cancer patients and fraternal twins have about 1.7 times the usual risk of developing breast cancer, while identical twins have about 4.4 times the usual risk. As for specific genetic mutations, according to the National Cancer Institute, those most associated with breast cancer risk occur in a pair of genes called BRCA1 and BRCA2. BRCA1 and BRCA2 are genes which are involved in the immune system's tumor suppression function; mutations in these genes lead to increased cancer susceptibility. Once identified, different mutations in these genes are given names that resemble a long string of code; these tell doctors and researchers where they are found and also distinguish them from other types of mutations that may occur in the same gene. In Sarah's case, doctors were able to identify a gene mutation in her maternal aunt called BRCA2-6174delT. They then looked for and, unfortunately, found the same mutation in Sarah. This mutation, along with a BRCA1 mutation called BRCA1-185delAG, happens to be common among Ashkenazi Jews. Studies have found that the frequencies for these mutations in the general Jewish population are 1.1 percent for the BRCA1-185delAG mutation and 1.5 percent for the BRCA2-6174delT mutation. The chances of having both of these mutations is about 1 in 50 among Ashkenazi Jews. These two mutations account for 25 percent of early-onset breast cancer and up to 90 percent of families with more than one case of both breast and ovarian cancer among Ashkenazi Jews:
(1) Comment has been made Niecee Schonberger
This is a very thorough explanation of the risks especially associated with Ashkenazi Jewish ancestry. Sharsheret is a national not-for-profit organization for Jewish women and their families facing breast or ovarian cancer. As Coordinator of the Genetics for Life program, I am happy to discuss genetic testing with any of your patients who have questions. I can be reached at 866-474-2774 and we also have a blog at www.sharhseret.blogspot.org, where you can find out about our programs and resources.Posted Wed, Jan. 6, 2010 at 3:11 pm EST
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