Lynch syndrome, or hereditary nonpolyposis colon cancer (HNPCC), is a familial cancer syndrome caused by an autosomal dominant mutation in DNA mismatch repair (MMR) genes. Affected individuals develop a small number of adenomas that can rapidly progress to colorectal cancer (CRC), resulting in a considerably earlier symptom onset compared to sporadic colorectal cancer. Individuals with Lynch syndrome are also at increased risk of developing other forms of cancer, especially endometrial, gastric, and ovarian cancer. Individuals are asymptomatic until they present with symptoms of advanced cancer. To identify those at high risk for Lynch syndrome, individuals are assessed according to the Amsterdam II criteria. Subsequent genetic analysis with detection of MMR mutations confirms the diagnosis. Treatment of CRC consists of surgical colectomy and immunotherapy. Preventative screening for colorectal cancer and associated tumors is recommended in individuals with family members known to have a Lynch syndrome gene mutation; it should occur every 1–2 years, starting at 20–25 years of age, or 2–5 years before the earliest recorded case of a tumor in the family.
- Sex: ♂ = ♀
- Average age of onset: 44 years
- Increased lifetime risk of associated cancers (by age 70)
Epidemiological data refers to the US, unless otherwise specified.
- Hereditary disease: autosomal dominant with varying penetrance
- Mutations in various DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2) cause microsatellite instability.
- Patients are usually asymptomatic until CRC develops (see ).
- Lynch syndrome-associated CRC usually affects the right (proximal) colon.
- Possibly extracolonic symptoms of associated cancers (see “Epidemiology” section above)
Subtypes and variants
- Muir-Torre syndrome
- : presence of Lynch syndrome-related CRC and brain tumors (especially gliomas)
The Amsterdam II criteria are used to identify individuals who are likely to be mutation carriers for Lynch syndrome.
|Amsterdam II criteria|
Presence of at least three relatives with a Lynch syndrome-associated cancer; all the following criteria should be present:
3-2-1 rule: (3 affected family members, 2 generations, 1 relative under 50 years of age).
|Revised Bethesda guidelines|
Individuals should be tested for MSI in the following situations:
- First test: tumor microsatellite instability (MSI) and/or immunohistochemical staining (IHC)
- Confirmatory test: germline testing via DNA sequencing
- For diagnosis of CRC, see .
Lynch syndrome typically manifests with colorectal cancer of the proximal colon, with only a few adenomatous polyps, in contrast to familial adenomatous polyposis, in which hundreds of adenomatous polyps are present.
- Immunotherapy with an immune checkpoint inhibitor (pembrolizumab or nivolumab) may be used for high MSI or mismatch repair deficient (dMMR) metastatic colorectal cancer. 
- For more specific guidelines regarding management, see .
- For women with Lynch syndrome, prophylactic hysterectomy and bilateral salpingo-oophorectomy should be offered when they are no longer of child-bearing age.
- Genetic testing is generally not recommended for at-risk individuals < 18 years of age.
- Genetic screening should be initiated 10 years before the earliest manifestation of the condition in the family.
Cancer screening: for Lynch syndrome patients with a confirmed mutation or who meet Amsterdam criteria
- Colonoscopy: every 1–2 years, starting at 20–25 years of age, or 2–5 years before the earliest recorded case of a tumor in the family (only if it occurred before 25 years of age), whichever comes first 
- Annual pelvic examination with transvaginal sonography and endometrial biopsy starting at 30–35 years of age or 3–5 years before the earliest reported case of a tumor in the family
- Annual upper endoscopy with biopsy of the gastric antrum starting at 30–35 years of age
- Annual physical exam and urinalysis
- Total colectomy: not generally recommended in patients with normal endoscopy