MSH2 Gene Mutation: Lynch Syndrome, Risks, and Screening

MSH2 (MutS Homolog 2) is a DNA mismatch repair gene. Its job is to help fix errors that happen when your DNA is copied before a cell divides. The MSH2 protein pairs with MSH6 to form a team that scans newly copied DNA for mistakes. When they find one, they recruit other repair proteins — including MLH1 — to correct it. This process keeps your DNA accurate and prevents cells from accumulating mutations that can lead to cancer.

MSH2 belongs to the Lynch syndrome gene family, alongside MLH1, MSH6, and PMS2. These four genes make up the mismatch repair (MMR) system. When any one of them is mutated, the repair system breaks down and cells begin to accumulate DNA errors at a much faster rate than normal. This condition is called Lynch syndrome, and it is the most common hereditary cause of colorectal and endometrial cancer.

MSH2 mutations are the second most common cause of Lynch syndrome after MLH1. Together, MLH1 and MSH2 account for the majority of Lynch syndrome cases. MSH2 mutations follow an autosomal dominant inheritance pattern, meaning you only need one copy of the mutated gene (from one parent) for it to affect your cancer risk. Approximately 1 in 400 people carry an MMR gene mutation, and MSH2 accounts for a significant proportion of those cases.

If you are concerned about hereditary cancer risk in your family, our guide on hereditary cancer screening explains how testing works and who should consider it.

Lynch syndrome is a hereditary condition caused by mutations in one of the mismatch repair genes (MSH2, MLH1, MSH6, or PMS2). It is the most common hereditary cause of both colorectal cancer and endometrial cancer. If you carry an MSH2 mutation, you have Lynch syndrome.

When MSH2 is not working properly, your cells cannot detect certain DNA copying errors. These unrepaired errors accumulate over time, especially in areas of DNA called microsatellites — short, repetitive sequences that are particularly prone to copying mistakes. This leads to a condition called microsatellite instability (MSI), which is a hallmark of Lynch syndrome tumors.

Microsatellite instability is clinically important for two reasons. First, it drives cancer development by allowing mutations to build up unchecked. Second, tumors with high MSI (MSI-High) tend to respond well to immunotherapy, specifically immune checkpoint inhibitors. This means that if an MSH2 carrier does develop cancer, there are targeted treatment options that can be highly effective.

Lynch syndrome is significantly underdiagnosed. An estimated 1 in 3 people who carry a Lynch syndrome mutation do not know they have it. Many Lynch syndrome carriers have no personal history of cancer and may not have an obvious family pattern because the condition can affect different organs in different family members. This is why genetic testing — not just family history alone — is essential for identifying carriers.

For a detailed overview of Lynch syndrome, including testing criteria and management strategies, see our comprehensive guide to Lynch syndrome.

MSH2 mutations carry some of the highest cancer risks among the Lynch syndrome genes. The risk varies by cancer type and is significantly elevated compared to the general population.

Colorectal cancer

• Lifetime risk for MSH2 carriers: approximately 40–60%
• General population lifetime risk: approximately 4%
• Colorectal cancer is the most common cancer in MSH2 carriers
• Cancer can develop at younger ages than typical — screening starts at age 20–25

Endometrial cancer (women)

• Lifetime risk for female MSH2 carriers: approximately 25–60%
• General population lifetime risk: approximately 3%
• Endometrial cancer is the second most common cancer in female MSH2 carriers

Ovarian cancer (women)

• Lifetime risk for female MSH2 carriers: approximately 10–20%
• General population lifetime risk: approximately 1.2%

Gastric cancer

• Elevated risk, estimated at approximately 5–10× the general population rate
• Upper endoscopy screening is recommended for MSH2 carriers

Urinary tract cancer

• Elevated risk, particularly for cancers of the renal pelvis and ureter
• Annual urinalysis is recommended to screen for early signs

Other cancers

• Small bowel cancer: modestly elevated
• Pancreatic cancer: modestly elevated
• Brain tumors (Turcot syndrome variant): rare but recognized association

Key takeaway: MSH2 carries some of the highest Lynch syndrome cancer risks, particularly for colorectal and endometrial cancer. Enhanced surveillance and prevention strategies are essential for carriers.

The goal of Lynch syndrome screening is to catch cancer early or prevent it entirely. NCCN guidelines provide detailed recommendations for MSH2 carriers, though your doctor may adjust these based on your personal and family history.

Colonoscopy

• Every 1–2 years starting at age 20–25
• Some high-risk families may need annual colonoscopy
• Start 2–5 years before the youngest colorectal cancer diagnosis in your family, whichever is earlier
• Frequent colonoscopy has been proven to reduce colorectal cancer mortality in Lynch syndrome carriers

Women: gynecologic surveillance

• Annual endometrial biopsy or transvaginal ultrasound starting at age 30–35
• Discuss risk-reducing hysterectomy and bilateral salpingo-oophorectomy (BSO) after childbearing is complete
• Risk-reducing surgery eliminates the risk of endometrial and ovarian cancer and is an important option for MSH2 carriers

All MSH2 carriers

• Upper GI endoscopy every 3–5 years starting at age 30–40 to screen for gastric and small bowel cancers
• Annual urinalysis to screen for urinary tract cancers
• Consider daily aspirin for colorectal cancer risk reduction (discuss with your physician)
• Cascade testing for first-degree relatives — parents, siblings, and children each have a 50% chance of carrying the mutation

Important: Screening recommendations are personalized based on your specific variant and family history. A licensed genetic counselor can help you build a screening plan tailored to your situation.

Lynch syndrome can be caused by mutations in any of four mismatch repair genes: MLH1, MSH2, MSH6, and PMS2. While all four cause Lynch syndrome, they differ in their cancer risk profiles and clinical implications.

MLH1 and MSH2: the highest-risk Lynch genes

• MLH1 and MSH2 carry the highest colorectal and endometrial cancer risks among the Lynch syndrome genes
• Both are associated with colorectal cancer risks of 40–60% or higher
• MLH1 is the most commonly mutated Lynch gene; MSH2 is the second most common
• Screening recommendations for MLH1 and MSH2 carriers are essentially the same

MSH6: lower colorectal risk, higher endometrial focus

• MSH6 carriers generally have lower colorectal cancer risk than MLH1 or MSH2 carriers
• Endometrial cancer risk may be proportionally higher relative to colorectal cancer in MSH6 carriers
• Cancers in MSH6 carriers tend to develop later in life compared to MLH1 or MSH2

PMS2: lowest cancer risks among Lynch genes

• PMS2 carriers have the lowest cancer risks of the four Lynch syndrome genes
• Colorectal cancer risk is estimated at 15–20%, significantly lower than MSH2
• Screening may start later and be less frequent than for MSH2 carriers

MSH2 and Muir-Torre syndrome

MSH2 mutations are also associated with Muir-Torre syndrome, a variant of Lynch syndrome that includes sebaceous skin tumors and internal organ cancers. If you have MSH2-associated Lynch syndrome and develop unusual skin growths, mention your MSH2 status to your dermatologist.

If you have received a positive MSH2 genetic test result, here are the steps to take:

1. Tell your gastroenterologist. Your colonoscopy schedule needs to change immediately. MSH2 carriers require colonoscopy every 1–2 years starting at age 20–25, which is far more frequent than standard screening. If you do not have a gastroenterologist, ask your primary care doctor for a referral.
2. Women: see a gynecologic oncologist. Endometrial cancer surveillance should begin at age 30–35, including annual endometrial biopsy or transvaginal ultrasound. Your gynecologic oncologist can also discuss risk-reducing surgery options after you have completed childbearing.
3. See a genetic counselor. Lynch syndrome has specific management protocols that differ from other hereditary cancer syndromes. A licensed genetic counselor can interpret your specific MSH2 variant, review your family history, and build a personalized surveillance plan.
4. Tell your first-degree relatives. Lynch syndrome affects the whole family. Each parent, sibling, and child has a 50% chance of carrying the same mutation. Cascade testing can identify which family members need enhanced screening — and which do not. Early identification of Lynch syndrome saves lives.
5. Know your rights. The Genetic Information Nondiscrimination Act (GINA) protects you from discrimination by health insurance companies and employers based on genetic test results. Life insurance, disability insurance, and long-term care insurance are not covered by GINA.

For general guidance on interpreting genetic test results, see our resource on understanding your genetic test results. If you have not been tested yet and want to find out whether hereditary cancer genetic testing is right for you, our free eligibility screener can help.

If you have been diagnosed with colorectal cancer, learn about hereditary testing after a colorectal cancer diagnosis. Relatives of someone with a confirmed MSH2 mutation can learn about how cascade genetic testing works.

Want to find out if you qualify for Lynch syndrome testing? Learn more about Lynch syndrome testing eligibility.

NCCN recommends MSH2 testing for individuals whose tumors show loss of MSH2 protein expression, those with microsatellite instability-high tumors, individuals meeting clinical criteria for Lynch syndrome, those with a personal or family history of multiple Lynch-associated cancers, or when a known MSH2 or EPCAM mutation exists in the family.

MSH2 mutations follow autosomal dominant inheritance, meaning each first-degree relative has a 50% chance of carrying the mutation. Lynch syndrome caused by MSH2 mutations is one of the most actionable hereditary cancer syndromes because colonoscopy surveillance dramatically reduces cancer mortality. Cascade testing is strongly recommended for all blood relatives, including children once they approach the recommended screening age (20–25). Identifying carriers before cancer develops allows for life-saving prevention.