The genetics of colon cancer

An inherited condition called Lynch syndrome can cause several types of cancer.

While screening for colon cancer usually begins at age 50, people with an inherited genetic condition called Lynch syndrome have an increased risk of developing colon cancer at an early age.

Discovering someone has Lynch syndrome helps doctors develop a personalized cancer screening schedule and recommend genetic testing for other family members, if necessary.

A genetic mutation that increases cancer risk

There are five genes associated with Lynch syndrome, also called hereditary nonpolyposis colon cancer, and a person has to inherit only one of these five gene changes to have the condition.

“The genes associated with Lynch syndrome are called mismatch repair genes,” said Lior Borovik, M.S., a certified genetic counselor at Sanford Health. “If you have a mutation in one of these mismatch repair genes, then they aren’t repairing genes with mistakes, and that causes more mutations in other genes, which can lead to cancer.”

A mutation in one of these mismatch repair genes does not guarantee a person will develop cancer; rather, that person’s risk is significantly higher.

“Depending on the gene inherited with Lynch syndrome, the risk of developing colon cancer can increase to anywhere from 15 percent up to 80 percent, as compared to 4 to 5 percent in the general population,” said Borovik.

“However, with Lynch syndrome, it’s not just the risk for colon cancer that increases. While colon and endometrial cancer are the main two cancers seen with Lynch syndrome, there is also an increased risk of ovarian cancer, stomach cancer, certain brain tumors, bile duct cancer, urinary tract cancer, cancer of the small intestines, pancreatic cancer and sebaceous cysts.”

Meeting with a genetic counselor

Anyone with a personal or family history of colon cancer or Lynch syndrome-related cancers can see a genetic counselor to determine if they should get genetic testing for Lynch syndrome.

Genetic testing may be suggested if a patient has:

  • Multiple close family members affected with same type (or associated) cancers
  • Relatives who developed cancer before age 50
  • Family members with more than one primary cancer
  • A generation-to-generation pattern of cancer within the family

Genetic counselors also explain the implications of genetic testing. There are many issues to take into account when considering genetic testing, including:

  • The benefits and harms of testing
  • Motivations for testing
  • Expectations about the results
  • The impact of a positive, negative or inconclusive result, and strategies for dealing with each
  • How genetic test results may affect careers, finances and insurance coverage

Risk factors determine screening plans

“While a patient with no risk factors would start colonoscopy screenings at age 50, the recommendation for a patient with Lynch syndrome is much earlier and more frequently,” said Borovik. For people with Lynch syndrome, this could mean having colonoscopies every year, starting at age 25.

People who have a family history of colon cancer should also start colonoscopies sooner than age 50.

When it comes to developing cancer screening plans, Borovik said, “we are evaluating a variety of risk factors, including types of cancer in the family, rare types of cancer, age of onset, number of family members who had polyps, how many polyps and ethnicity.

“These pieces of information are important because they can help us with our assessment to determine if a family might have hereditary cancer, such as Lynch syndrome or other hereditary colorectal cancer, and can influence when a patient should be screened.”

Posted In Cancer, Genetics, Health Information, Healthy Living

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