Lynch syndrome is an inherited condition that increases a person’s risk of developing colorectal cancer and other forms of cancer before the age of 50 years. Doctors may also refer to it as hereditary nonpolyposis colorectal cancer (HNPCC).

According to the National Institutes of Health (NIH), Lynch syndrome is responsible for 3–5% of colorectal cancers in the United States.

People who have Lynch syndrome have the following lifetime risk of these types of cancer:

  • colorectal cancer: 52–82%
  • endometrial cancer: 25–60%
  • stomach cancer: 6–13%
  • ovarian cancer: 4–12%

Lynch syndrome also increases the likelihood of the following cancers developing:

  • liver
  • kidney
  • brain
  • skin
  • gallbladder
  • small intestine
  • urinary tract

Lynch syndrome is the most common inherited cancer syndrome, affecting as many as 1 in every 370 people in Western countries.

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Stomach pain and constipation are symptoms of Lynch syndrome.

People who have Lynch syndrome can develop noncancerous growths in the colon. These benign growths are also called polyps.

People with Lynch syndrome may develop colon polyps at an earlier age than people without this condition. However, Lynch syndrome does not affect the number of colon polyps that develop.

Lynch syndrome can also lead to other symptoms and complications, including:

As a genetic disorder, Lynch syndrome occurs when a person inherits an altered or mutated gene.

The genes that researchers have associated with Lynch syndrome include MLH1, MSH2, MSH6, PMS2, and EPCAM. These genes help repair errors in DNA that occur during cell division.

Errors in DNA can lead to abnormal cell development and uncontrolled cell growth, which can result in cancer.

Everyone inherits two copies of each gene: one from each parent. Lynch syndrome is an inherited condition that follows an autosomal dominant pattern. This pattern means that people only need to inherit one copy of the altered gene to develop Lynch syndrome.

Although having Lynch syndrome can increase a person’s risk of developing certain types of cancer, not everyone who has Lynch syndrome will develop cancer.

People who have Lynch syndrome only develop cancer when a second mutation occurs in the unmutated gene. However, the second mutation only affects the genes present in the cancer cells.

The following factors may indicate Lynch syndrome:

  • developing colorectal or endometrial cancer before 50 years of age
  • developing two or more cancers relating to Lynch syndrome at any age
  • having one or more relatives with a Lynch syndrome cancer
  • having one or more relatives whom doctors have identified as having a genetic mutation that links to Lynch syndrome

A doctor can determine whether a person has a genetic mutation that has an association with Lynch syndrome by analyzing their DNA. Before offering genetic testing, a doctor will usually review the individual’s personal and family medical history to determine their likelihood of having Lynch syndrome.

People should see a doctor if they:

  • are concerned about their risk of colorectal cancer or other Lynch syndrome cancers
  • have a personal or family history of colorectal cancer
  • have one or more relatives who have Lynch syndrome

People who have Lynch syndrome can learn more about the condition by seeing a genetic counselor.

A genetic counselor is a healthcare professional who specializes in identifying a person’s risk of inherited conditions. They also provide education and counseling services to help people understand and live with genetic conditions.

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Without treatment for colon polyps, a person may experience anemia and fatigue.

Developing colorectal cancer is the main complication of Lynch syndrome.

However, people can also develop noncancerous colon polyps. If a person does not receive treatment, colon polyps can cause the following symptoms:

  • stomach pain
  • constipation or diarrhea
  • changes in the color or texture of stools
  • anemia
  • fatigue

Learn more about colon polyps here.

The type of treatment for Lynch syndrome varies depending on whether a person shows signs of colorectal cancer.

People who have Lynch syndrome but have not developed cancer may want to schedule regular colonoscopies and cancer screenings.

During a colonoscopy, a doctor examines the colon and rectum for signs of abnormal cell growth. It is often possible to remove colon polyps during this procedure.

Some people may opt to undergo a prophylactic colectomy, which is the removal of the colon before colon cancer develops.

For people who have Lynch syndrome and have developed colorectal cancer, the following treatments are available:

  • Polypectomy: a surgical procedure in which a doctor removes cancerous polyps lining the colon.
  • Colectomy: a surgical procedure that involves removing all or part of the colon as well as any affected lymph nodes.
  • Ablation: a procedure in which a doctor uses radiofrequency waves, including microwaves, to destroy small tumors.
  • Cryosurgery: a procedure that involves a doctor using a thin metal probe to administer cold gas to the surface of a tumor to kill the cancer cells.
  • Embolization: a technique that requires a doctor to insert a thin tube into an artery to block the flow of blood to a large tumor.

The Centers for Disease Control and Prevention (CDC) recommend genetic testing for anyone who has recently received a colorectal cancer diagnosis, regardless of their age or family medical history.

Doctors use two different types of procedure for screening colorectal tumors:

Immunohistochemistry (IHC) screening

Doctors use this screening test to identify missing proteins in tumor samples. A tumor sample that does not contain MSH2 or MSH6 proteins strongly suggests that a person has Lynch syndrome.

Microsatellite instability screening (MSI)

A microsatellite refers to a section of copied DNA that is a different length than the same part of the original DNA.

The MSI screening test examines the length of DNA microsatellites in tumor samples. People who have a high MSI test result are likely to have Lynch syndrome.

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Managing risk factors, such as diet and physical activity, can lower a person’s risk of developing colorectal cancer.

Although there is no way to prevent colorectal cancer completely, people can lower their risk by getting regular colorectal cancer screenings.

According to the American Cancer Society, precancerous polyps can take 10–15 years to develop into colorectal cancer. Screening can allow people to spot these polyps early and take action before they can develop further.

Managing certain risk factors, such as diet and physical activity, can also lower a person’s risk of developing colorectal cancer.

Research has linked obesity to several different cancers, including:

  • colorectal
  • esophageal
  • gallbladder
  • stomach
  • kidney
  • liver
  • breast
  • ovarian

In a 2019 review article, researchers found a potential molecular link between obesity, insulin resistance, and colorectal cancer risk. The researchers cited numerous studies that found altered microRNA in both animal and human fat tissue.

MicroRNA is a type of RNA that plays a role in regulating the expression of genes in DNA. Changes that affect microRNA can result in the development of abnormal or cancerous cells.

The researchers believe that chronic low grade inflammation due to obesity and insulin resistance may be responsible for the microRNA changes.

The authors of a 2015 review article concluded that obesity increases the risk of colorectal cancer by 19%, while regular physical activity reduces the risk by 24%.

Although Lynch syndrome can significantly increase a person’s risk of developing colorectal, stomach, endometrial, and ovarian cancer, not everyone who has Lynch syndrome will develop cancer.

Lynch syndrome causes a small percentage of all colorectal cancers, so health organizations such as the CDC feel that genetic testing will not provide additional benefits to people who have not received a diagnosis of colorectal cancer.

The average 5 year relative survival rate for all stages of colorectal cancer is 64%, according to the American Cancer Society. Survival rates vary according to the stage and location of the cancer, with localized cancer having a much higher survival rate than cancer that has spread.

In a 2019 study, researchers from Shanghai in China found strong evidence to suggest that attending regular cancer screenings and colonoscopies can lead to earlier diagnosis and better treatment outcomes.

People who have Lynch syndrome or a family history of colorectal cancer can speak with their doctor about the potential costs and benefits of genetic testing. People can also schedule regular colonoscopies and cancer screenings.