When Color launched their first test in April 2015, it included 19 genes for hereditary breast and ovarian cancer. People were really excited about it, but one nurse practitioner kept asking us to add more genes, particularly those for hereditary colon cancer. She was so passionate about it that at one point she actually yelled, “Don’t forget about the colon!”
March is Colon Cancer Awareness Month. While it doesn’t typically get as much attention as other cancer awareness months, despite it being on the rise among young adults, colon cancer has been on my personal radar since I found out that I and some of my family members have an increased chance to develop colon cancer due to an inherited genetic mutation.
When I was being trained as a genetic counselor, my cancer rotation was focused on hereditary gastrointestinal cancers, such as colon cancer. I quickly learned that colon cancer is pretty common — 1 in 24 women and 1 in 23 men will develop colon cancer in their lifetime — but also very preventable; colonoscopy is associated with a greater than 60% reduction in both colorectal cancer and in deaths from colorectal cancer¹.
Mutations in many different genes are known to increase a person’s risk to develop colon cancer in their lifetime. One group of genes causes Lynch Syndrome, which is characterized by increased risk for colon, uterine, ovarian and other types of cancer. It’s actually more common for someone to have a gene mutation that causes Lynch syndrome (1 in 230) than a mutation in the well-known BRCA1 or BRCA2 genes (1 in 400) that cause an increased risk for breast and ovarian cancer. Nonetheless, many more people are offered genetic testing for BRCA1 and BRCA2 than for Lynch.
The risk of colon cancer caused by an inherited genetic mutation can vary by gene. For example, having a mutation in a gene that causes Lynch syndrome can increase a person’s chance to develop colon cancer up to 50% by age 70, and having a single mutation in a gene called MUTYH can increase a person’s chance to develop colon cancer to about 11–14% by age 80. This can be compared to the average risk of 2.8–3.4% to develop colorectal cancer by age 80.
Several months ago, I found out that I have a single MUTYH gene mutation. I don’t have any relatives who’ve had colon cancer. In fact, the only family history of cancer I have is a paternal grandfather who had lymphoma in his 60s.
Learning I have a gene mutation also has implications for my family members — my mom, dad, sister and brother all had a 50% chance of having the same mutation. My children, should I decide to have any, will also have a 50% chance of having this mutation. My parents were tested and we learned that this mutation came from my father’s side. My sister and brother are still deciding if they want to have genetic testing. My father has two sisters who are currently undergoing testing to see if they have this MUTYH mutation. If they do have it, they will also need more frequent colon cancer screening and would want to let their children know, as they could have passed this mutation to my cousins.
There is one other thing that is a little different about MUTYH: if someone has a mutation in each copy of MUTYH (one from each parent), they have a much higher chance of developing colon cancer and need to start screening in their 20s. So, when one person has a single MUTYH mutation, I encourage them to consider telling their reproductive partner, so they can consider getting tested as well (if both partners have MUTYH mutations, there’s a 25% chance that each of their children would have two mutations and a much higher risk of colon cancer).
While having a MUTYH mutation doesn’t increase my colon cancer risk as high as some other gene mutations would, it is recommended that I begin my colon cancer screening earlier (at age 40 rather than age 50) and repeat that screening a little more often than someone who is at average risk for colon cancer (every 5 years rather than every 10). Even people who don’t have a mutation in a gene linked to increased colon cancer risk still have a 4.2–4.8% chance to develop colon cancer by age 95 and there are many factors besides genetics that can influence a person’s risk for colon cancer. So, this March I encourage you to speak with your provider about screening for colorectal cancer.
- Pan J, Xin L, Ma Y, et al. Colonoscopy Reduces Colorectal Cancer Incidence and Mortality in Patients With Non-Malignant Findings: A Meta-Analysis. Am J Gastroenterol 2016; 111:355–365.