Different Breast Cancer Genes Identify Different Risks, Not All Lead to Preventative Mastectomy
We have all been affected by cancer, whether it be a new diagnosis in a friend, relative, coworker, pet, or even a personal diagnosis. Breast cancer is especially common in this country, with one in eight women developing breast cancer by age 70. Researchers have identified multiple genes that can increase the risk for breast cancer when these genes have a mistake (also called a mutation) in them. The most common of these breast cancer genes are BRCA1 and BRCA2, made famous by the actress Angelina Jolie, who wrote about her journey in testing BRCA1 positive. Having a mutation in one of the BRCA genes can significantly increase the risks for several cancers, with the highest being breast cancer, leading some women to consider removing their breasts preventively.
In fact, more and more women are choosing to have mastectomies based on their genetic risk for breast cancer. According to one study, up to 50% of women with BRCA mutations are choosing to have preventative mastectomy (Padamsee, T.J. et al). Since the discovery of the BRCA genes, several other genes have been found that can increase the risk for breast cancer in those with a mutation. The number of people being tested for these genes has increased in the past few years, leading to more mutations found in newer breast cancer genes, and therefore more people questioning whether they should also consider a mastectomy.
However, the risk to develop breast cancer is not equal among these genes. Geneticists tend to put breast cancer genes in different categories of risk such as “low”, “moderate” or “high” risk. For example, the BRCA genes are high risk genes, since the chance to develop breast cancer is up to 56-87%. Because the risks are significantly increased (although not 100%), women who have a BRCA1 or BRCA2 mutation may opt to have a mastectomy to decrease their risk. Alternatively, increased screening with mammogram and breast MRIs is an option to catch something early, or some women choose to take medications to help decrease the risk for breast cancer.
While there are clearly some high-risk genes for which preventative mastectomy is an option, there are also several low and moderate risk genes for which there are currently no recommendation for mastectomy. Genes such as CHEK2, PALB2 and NBN are more recently described with less data on the lifetime risk they cause. These genes are more often called low or moderate risk genes, meaning the chance to develop breast cancer is increased from the average women’s risk, but either the exact risk is unclear at this time or it is lower than the high-risk genes. Therefore, when women have a mutation in a low or moderate risk gene, the risk for breast cancer is increased, but there may not be enough evidence to state that preventative mastectomy is warranted (based on National Comprehensive Cancer Network, or NCCN, guidelines).
To compare these risks, imagine there are 100 women in a room and 12 of them develop breast cancer in their lifetime. This is the non-genetic risk, which is considered “sporadic” cancer. Now, consider if all the women in that room had a mutation in a BRCA gene. This would mean that up to 80 out of those 100 women (or 80% of them) would develop breast cancer. However, if all of the women in that room had a low or moderate risk gene mutation, approximately 25 to 30 of them would develop breast cancer in their lifetime. That means when women have these low or moderate risk gene mutations, there is approximately a 65-70% chance they would NOT develop breast cancer.
So why are so many women still considering mastectomies when they have a low or moderate risk gene mutation? It may be that there is not enough knowledge regarding the different categories of breast cancer risk, and therefore, some providers may be erroneously following high risk recommendations. This could lead to many unnecessary surgeries, when instead women with mutations in these low or moderate risk genes should base their decision regarding mastectomy on any personal factors (like precancerous breast cells) or having a strong family history of breast cancer. Instead of surgery, individuals with these low or moderate risk gene mutations may qualify for a high risk breast screening protocol – annual mammograms beginning at age 40, and consideration of annual breast MRI screening.
Although there is currently limited data on the risks for low/moderate genes, this is constantly being studied and we are learning more every day. The ever-changing complexity of genetic risk for breast cancer highlights the importance of speaking with a genetics expert to fully understand and assess the risk. To find a genetic counselor in person, visit the National Society of Genetic Counselors website, www.nsgc.org. Genetic counseling via phone and video is also available from InformedDNA.
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