Living with cancer blog

Colorectal cancer risk: genes, the environment and family history

By Sheryl M. Ness, R.N. January 29, 2014

Mayo Clinic's Dr. Lisa Boardman is a GI specialist and researcher interested in how colorectal cancer develops. She's especially interested in the connection between an individual's genes, environment and family history. All play a part in a person's risk for developing colorectal cancer. I asked Dr. Boardman a few questions related to colorectal cancer and individual risk for a discussion on the blog.

Q: What's the most important thing that people should know about colorectal cancer screening?

A: Colorectal cancer is a disease that we can actually prevent in most people with colon cancer screening tests. Screening can include stool tests like fecal occult blood tests, or the fecal immunochemical test (FIT), stool DNA tests, flexible sigmoidoscopy, CT scan colonography or colonoscopy. The goal of colon screening is to catch colorectal cancer early enough so that a person will have a better cure rate than if he or she waited until the cancer made that person develop symptoms.

Colorectal cancer begins when a polyp (or polyps) grows in the colon or rectum, and over time transforms into cancer. If we remove a polyp (or polyps) through colonoscopy, a person's chance of developing colorectal cancer will be greatly decreased. We know that certain people are at increased risk. It's important to understand who needs to be screened and at what age. One size doesn't fit all for colorectal cancer screening.

Q: What about my family history?

A: We know that certain people are at higher risk because of what's happening in their family. If you have a first degree relative (such as your parents, brothers or sisters, or child), you're at an increased risk. Also, the age in which your family member developed colon cancer is important to note (especially under age 60).

Q: What are some of the genetic conditions that would put me at a higher risk?

A: Another risk factor for colorectal cancer is genetic mutations that can be inherited through the generations. A small percentage of colorectal cancer results from hereditary gene mutations. Some of the hereditary colorectal cancer syndromes are autosomal dominant, meaning you need to inherit only one defective gene from either one of your parents and that both men and women are equally at risk for inheriting the defective gene. If one parent has the mutated gene, you have a 50 percent chance of inheriting the mutation. Although inheriting a defective gene greatly increases your risk, not everyone with a mutated gene develops cancer. A few genetic conditions that may put you at increased risk for colorectal cancer include:

  • Familial adenomatous polyposis (FAP) — This is a rare, hereditary disorder that causes you to develop hundreds, even thousands, of polyps in the lining of your colon beginning during your teenage years. If these go untreated, the risk of developing colorectal cancer is nearly 100 percent, usually before age 40. In some cases, genetic testing can help determine whether you're at risk of the disease. Gardner’s syndrome is a variation of FAP caused by the same gene that causes FAP, but you may also develop noncancerous tumors in other parts of your body, including your skin (sebaceous cysts and lipomas), bone (osteomas) and abdomen (desmoids). In people with attenuated FAP (AFAP), people develop fewer polyps (<100) and the risk for colorectal cancer is less than for those with FAP.
  • MYH-associated polyposis (MAP) — This inherited condition is similar to FAP. People with MAP often develop multiple adenomatous polyps and colorectal cancer at a young age. Genetic testing can help determine whether you're at risk of MAP, which is caused by mutations in the MYH gene.
  • Lynch syndrome — This condition, also called hereditary nonpolyposis colorectal cancer (HNPCC) is the most common form of inherited colorectal cancer. People with Lynch syndrome tend to develop relatively few colorectal polyps, but those polyps can quickly become malignant. People with Lynch syndrome may have tumors in other organs, including the stomach, uterus, ovaries, small intestine, and genitourinary tract but most commonly in the colon or rectum.

Q: What about my environment or lifestyle puts me at higher risk for colorectal cancer?

A: Some factors that contribute to the development of colorectal cancer include:

  • Age (50 and older)
  • Sedentary lifestyle
  • Smoking
  • Alcohol use
  • Increased weight

Q: When is it important to see my doctor if I am concerned about colorectal cancer?

A: See your doctor if you notice the following signs and symptoms:

  • Abdominal pain
  • Blood in your stool
  • A change in your bowel habits that lasts longer than a week

You should be screened regularly for polyps if:

  • You're age 50 or older
  • You have risk factors, such as a family history of colorectal cancer — in some cases, high-risk individuals should begin regular screening much earlier than age 50

Look for continued discussion on colon cancer and genetics in the following weeks on the Living with Cancer blog. Do you have questions about your personal risk for developing colon cancer? Feel free to comment on the blog.


Sheryl M. Ness, R.N.

Jan. 29, 2014