Lynch syndrome: the genetics of colon cancer

Screening for colon cancer should start at age 45, but for people with an inherited genetic condition called Lynch syndrome, it should be done much earlier. They have an increased risk of developing colon cancer at an early age.

Finding someone with Lynch syndrome helps doctors develop a personalized cancer screening schedule. If necessary, they will recommend genetic testing for other family members.

Genetic mutation that increases the risk of cancer

Five genes are associated with Lynch syndrome, also called hereditary non-polyposis colon cancer. A person must inherit only one of the five gene changes to have the disease.

“The genes associated with Lynch syndrome are called mismatch repair genes,” said Lior Borovik, M.D., certified genetic consultant at Sanford Health. “If you have a mutation in one of these mismatch repair genes, then they don’t repair the mismatched genes, 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 that a person will develop cancer; rather, that person’s risk is significantly higher.

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

“However, with Lynch syndrome, it is not only the risk of colon cancer that increases. Colon cancer and endometrial cancer are the two main cancers seen in Lynch syndrome. However, there is also an increased risk of ovarian or stomach cancer, certain brain tumors, bile duct cancer, urinary tract cancer, small intestine cancer, pancreatic cancer, and sebaceous cysts.”

How is Lynch syndrome diagnosed?

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

“People with Lynch syndrome are at an extremely high risk of developing colon cancer than the general population,” said Brett Balone, MD, board certified in gastroenterology, hepatology, and internal medicine.

Approximately 3 to 5% of colon cancers are caused by Lynch syndrome. A complicating factor, according to Dr. Baloun, is that Lynch syndrome does not show warning signs. Its early identification is not confirmed by a high-tech test. It requires dialogue.

“It’s all about good conversation and a good story,” he said. “When you visit your doctor, talk about whether you have a family history of cancer. It all starts with knowing your family history and sharing it with your doctor.”

Meeting with a geneticist

Genetic testing may be offered if the patient has:

  • Several close relatives have the same type of cancer (or related ones)
  • Relatives who developed cancer before age 50
  • Family members with more than one primary cancer
  • Family pattern of cancer from generation to generation

Genetic consultants also explain the implications of genetic testing. There are many issues to consider when considering genetic testing, including:

  • The benefits and harms of testing
  • Motives for Testing
  • Results Expectations
  • The impact of a positive, negative, or inconclusive outcome and strategies for dealing with each.
  • How genetic test results can affect career, finances and insurance coverage

Risk Factors Determine Screening Plans

Patients without risk factors should start screening for colorectal cancer at age 45, but patients with Lynch syndrome should be screened much earlier and more frequently. For people with Lynch syndrome, this may mean an annual colonoscopy starting at age 25.

People who have a family history of colon cancer should also start a colonoscopy earlier than age 45. 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 examined.”

Accelerated cell mutation

In Lynch syndrome, cells that normally die and are replaced instead mutate into adenomas with the potential to develop into colon cancer. For most, the process of developing cancer can take seven to ten years. However, people with Lynch syndrome have accelerated cell mutation and may develop cancer within 24 to 35 months.

The possibility of a patient having Lynch syndrome is most often identified during visits to primary care physicians. Patients can then be referred to specialists such as Dr. Balun.

“It doesn’t have to be the person identified as a Lynch carrier, but it could have been other generations of their family with endometrial cancer, colon cancer, pancreatic cancer, or other cancers associated with Lynch syndrome,” Dr. Balun said. . . “This story provides a clue that the patient may be a Lynch carrier and we should consider genetic testing.”

Influence of decades

While this is the most common hereditary cancer syndrome, Dr. Baloun said Lynch is still underestimated. It is little known and it may have affected families for decades.

Since there is no gene therapy for Lynch syndrome, it is treated by identifying genetic mutations. Aggressive screening and possible surgery fight developing cancer.

“When someone is diagnosed with Lynch syndrome, it all 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 a colonoscopy when she is 20 years old. Then we do an upper endoscopy every two years and a colonoscopy every year. It’s really intense viewing, unlike the average person.”

Understanding of Lynch syndrome is growing along with greater understanding of the role that genetics play in the disease.

“Nothing beats actually looking at the genes and being able to tell a person that he or she is a Lynch carrier and that it’s time to talk about screening,” Dr. Baloun said.

The key for healthcare professionals is to distinguish between potentially associated hereditary cancer syndromes and more sporadic colon cancers. These non-hereditary cancers are much more common, accounting for 70-80% of colon cancers. The remaining 20-30% can be attributed to hereditary cancer syndromes affecting the colon, of which Lynch is the most common.

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