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Allen KamravaMD · MBA · FACS · FASCRS

Colon and Rectum

Hereditary Non-Polyposis Colorectal Cancer (Lynch Syndrome)

Lynch syndrome is an inherited disorder that significantly increases the risk of developing colorectal cancer and other cancers at a young age.

Reviewed by Allen Kamrava, MD, MBA, FACS, FASCRS · Last reviewed 2025-10-12

Overview

What is Lynch Syndrome?

Lynch syndrome, also known as Hereditary Non-Polyposis Colorectal Cancer (HNPCC), is the most common inherited cause of colorectal cancer, accounting for about 3% of all cases. It is an autosomal dominant genetic condition, meaning a person only needs to get the gene from one parent to inherit the risk. Lynch syndrome does not cause a large number of polyps like other syndromes, but the polyps that do develop can turn into cancer much more quickly than in the general population. The condition also increases the risk of several other cancers, particularly uterine (endometrial) cancer in women, as well as cancers of the stomach, ovaries, small intestine, urinary tract, and others.

Symptoms

What are the signs of Lynch Syndrome?

Lynch syndrome itself does not cause symptoms. The signs of the syndrome are based on a personal and family history of cancer. Key features that suggest Lynch syndrome include:

  • Colorectal or uterine cancer diagnosed before age 50.
  • Multiple close relatives with Lynch-associated cancers (colorectal, uterine, stomach, ovarian, etc.).
  • Multiple Lynch-associated cancers in the same individual, either at the same time or over a lifetime.
  • A colorectal tumor that shows signs of mismatch repair deficiency on testing.

Causes & risk factors

What causes Lynch Syndrome?

Lynch syndrome is caused by an inherited mutation in one of several genes responsible for mismatch repair (MMR). These MMR genes (most commonly MLH1, MSH2, MSH6, and PMS2) act like a spell-checker for your DNA, correcting errors that occur when cells divide. When one of these genes is mutated, this repair system doesn't work correctly. As a result, errors accumulate in the DNA at a much faster rate, which can lead to the uncontrolled cell growth that causes cancer. This genetic instability is known as microsatellite instability (MSI).

When to see a doctor

When should I consider genetic testing?

You should talk to your doctor or a genetic counselor about testing for Lynch syndrome if you have a personal or family history that is suspicious for the condition. This includes:

  • A personal diagnosis of colorectal or uterine cancer before age 50.
  • A known Lynch syndrome mutation in your family.
  • A family history that meets the Amsterdam criteria or other clinical guidelines for suspected HNPCC.
  • If you are diagnosed with colorectal cancer, your tumor should be automatically tested for mismatch repair deficiency (MSI or IHC), which can indicate the possibility of Lynch syndrome.

Diagnosis & tests

How is Lynch Syndrome diagnosed?

The diagnosis of Lynch syndrome is a two-step process:

  1. Tumor Testing: The first step is to test a colorectal or uterine tumor for signs of mismatch repair deficiency. This is done with either Immunohistochemistry (IHC), which looks for the absence of MMR proteins, or a Microsatellite Instability (MSI) test, which looks for changes in DNA length. If the tumor shows signs of deficiency, it suggests that Lynch syndrome might be the cause.
  2. Genetic Testing: The definitive diagnosis is made by a blood test that looks for a germline (inherited) mutation in one of the MMR genes. This is usually done after a suspicious tumor test or if there is a very strong family history.

Treatment

How does a Lynch Syndrome diagnosis affect cancer treatment?

If you are diagnosed with colorectal cancer and are found to have Lynch syndrome, your surgical options may be different. Because you are at a very high risk (up to 60%) of developing a second, new colorectal cancer in the future, a more extensive surgery may be recommended.

  • For Colon Cancer: Instead of removing only the segment of the colon with the cancer (segmental colectomy), a total abdominal colectomy (removing the entire colon but leaving the rectum) is often recommended to prevent future colon cancers.
  • For Rectal Cancer: The decision is more complex, but a proctocolectomy (removing the entire colon and rectum) may be considered.
  • For Women: A prophylactic hysterectomy and oophorectomy (removal of the uterus and ovaries) is often recommended to prevent uterine and ovarian cancer, and can sometimes be performed at the same time as the colon surgery.

Self-care

How is Lynch Syndrome managed?

Management of Lynch syndrome focuses on intensive surveillance to detect cancers at their earliest, most treatable stage.

  • Colonoscopy: This is recommended every 1 to 2 years, starting between ages 20 and 25, or 2-5 years earlier than the youngest age of colorectal cancer diagnosis in the family.
  • For Women: Annual screening for uterine and ovarian cancer should begin between ages 30 and 35, often with a transvaginal ultrasound and endometrial biopsy.
  • Other Cancers: Screening for other Lynch-associated cancers, such as upper endoscopy for stomach cancer or urinalysis for urinary tract cancer, may be recommended based on your specific gene mutation and family history.

Frequently asked questions

Does everyone with Lynch syndrome get cancer?
No, but the risks are very high. The lifetime risk of developing colorectal cancer can be up to 70-80%, and for women, the lifetime risk of uterine cancer can be up to 60%, depending on the specific gene mutation. Intensive screening dramatically reduces the risk of dying from these cancers.

If I have Lynch syndrome, what does that mean for my children?
Because Lynch syndrome is an autosomal dominant condition, each of your children has a 50% chance of inheriting the mutated gene. They should be offered genetic counseling and testing, usually starting in their late teens or early 20s, so they can begin appropriate screening if they have the mutation.

References

Watch: Hereditary Non-Polyposis Colorectal Cancer (Lynch Syndrome): Understanding Your Family's Cancer Risk

Play: Hereditary Non-Polyposis Colorectal Cancer (Lynch Syndrome): Understanding Your Family's Cancer Risk

This explainer details Lynch syndrome, which is the most common type of hereditary colorectal cancer, though it accounts for only about 3% of all colorectal cancer cases. It is a genetic condition that increases cancer risk. The root cause is a glitch in a "spell checker" gene within the mismatch repair (MMR) system, allowing genetic typos to accumulate and eventually leading to cancer. Current guidelines recommend universal screening (testing the tumor tissue) for everyone diagnosed with colorectal cancer to identify the faulty gene. Lynch syndrome carries the highest risk for colorectal cancer and the second highest risk for endometrial/uterine cancer in women. Management involves aggressive, proactive surveillance: colonoscopies start in the early 20s and are performed every 1 to 2 years, which can significantly improve life expectancy. Lynch-related cancers are often highly susceptible to modern immunotherapy drugs.

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