Lynch syndrome: The genetics of colon cancer

This inherited condition can cause several types of cancer.

older man and woman smiling

Screening for colon cancer usually begins at age 50. But it’s much earlier for people with an inherited genetic condition called Lynch syndrome. They 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. They will recommend genetic testing for other family members, if necessary.

A genetic mutation that increases cancer risk

Five genes are associated with Lynch syndrome, also called hereditary nonpolyposis colon cancer. A person has to inherit only one of the 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.

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“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. Colon and endometrial cancer are the main two cancers seen with Lynch syndrome. However, there is also an increased risk of ovarian or stomach cancer, certain brain tumors, bile duct cancer, urinary tract cancer, cancer of the small intestines, pancreatic cancer and sebaceous cysts.”

How is Lynch syndrome diagnosed?

Open communication between patients and providers increases awareness about the condition. This is crucial to stopping cancer development through early screening and intervention.

“Individuals with Lynch syndrome are at an extremely higher risk of developing colon cancer than the general population,” said Brett Baloun, M.D., board-certified in gastroenterology, hepatology and internal medicine.

About 3 to 5 percent of colon cancers are caused by Lynch syndrome. A complicating factor, Baloun said, is that Lynch syndrome doesn’t present with warning signs. Its early identification isn’t indicated through a high-tech test. It requires a dialogue.

“It’s all about a good conversation and a good history,” he said. “When seeing your primary care doctor, talk about if you have a family history of cancer. It all starts with the awareness of your family history and making sure that’s shared with your physician.”

Meeting with a genetic counselor

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. Borovik said several risk factors are involved:

  • Types of cancer in the family
  • Rare types of cancer
  • Age of onset
  • Number of family members who had polyps
  • How many polyps
  • Ethnicity

“These pieces of information can help us determine if a family might have hereditary cancer,” he said. “They can influence when a patient should be screened.”

Accelerated cell mutation

With Lynch syndrome, cells that would typically die and be replaced instead mutate into adenomas with the potential to grow into colon cancer. For most, the process of developing cancer can take seven to 10 years. However, people with Lynch syndrome experience accelerated cell mutation and can develop cancer within 24-35 months.

The possibility of a patient having Lynch syndrome is identified most often through visiting with primary care doctors. Patients can then be referred to specialists like Dr. Baloun.

“It doesn’t have to be that individual who is identified as a Lynch carrier, but it could have been other generations of their family having endometrial cancer, colon cancer, pancreatic cancer or other cancers associated with Lynch syndrome,” Dr. Baloun said. “That history provides the clue that a patient might be a carrier for Lynch, and we should consider genetic testing.”

Decades-long impact

Although it’s the most common hereditary cancer syndrome, Dr. Baloun said Lynch is still underestimated. It isn’t well known and it could have been affecting families for decades.

Because no gene therapies exist for Lynch syndrome, it is fought through identification of genetic mutations. Aggressive screening and potential surgical intervention fight the developing cancer.

“When somebody gets diagnosed with Lynch syndrome, it really comes down to screening,” Dr. Baloun said. “For example, if a woman with a family history of Lynch syndrome is referred to me, we start screening for colonoscopy in her 20s. And then we do upper endoscopies every two years and colonoscopy every year. It’s really intense screening as opposed to an average person.”

Understanding of Lynch syndrome is growing alongside a greater understanding of the role that genetics play in disease. “Nothing compares to actually looking at the genes and being able to tell a person that he or she is a carrier for Lynch and that it’s time to talk about screening,” Dr. Baloun said.

The key for providers is drawing distinctions between potentially linked inherited cancer syndromes versus cancers of the colon that are more sporadic. These non-inherited cancers are far more common, comprising 70 to 80 percent of cancers of the colon. The remaining 20 to 30 percent can be traced back to hereditary cancer syndromes affecting the colon, of which Lynch is the most common.

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Posted In Cancer, Genetics, Health Information, Healthy Living

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