Lynch Syndrome: Key Insights Into Risks, Skin Signs & Diagnosis
Inherited cancer syndrome with sebaceous skin tumours and high risk of colorectal and other cancers; early detection key.
Author: Dr. Reviewed by Expert Dermatologist
Lynch syndrome, also known as hereditary non-polyposis colorectal cancer (HNPCC), is the most common hereditary colorectal cancer syndrome. It is characterised by germline mutations in DNA mismatch repair (MMR) genes leading to microsatellite instability (MSI) and a significantly elevated lifetime risk of colorectal cancer (up to 80%), endometrial cancer (up to 60%), and a range of other malignancies. What is unique about Lynch syndrome in dermatology is its association with cutaneous neoplasms, particularly in the Muir-Torre syndrome (MTS) variant, where sebaceous tumours and keratoacanthomas may be the presenting feature. Skin lesions may be one of the first signs of Lynch syndrome and represent 3–5% of the extracolonic cancers.
What is Lynch syndrome?
Lynch syndrome affects approximately
one in 350 individuals
across white, Asian, and African populations. It follows an autosomal dominant inheritance pattern with high but age-dependent penetrance. Germline pathogenic variants in one of four MMR genes — MLH1, MSH2, MSH6, or PMS2 — or the neighbouring EPCAM gene account for nearly all cases. These mutations impair the DNA mismatch repair system, causing replication errors that accumulate as MSI-high tumours.Muir-Torre syndrome (MTS) is a phenotypic variant of Lynch syndrome occurring in 1–2% of cases, more commonly in males (3:2 ratio) with skin manifestations appearing at an average age of 53 years (range 21–88 years). MTS is strongly associated with MSH2 mutations (90%), with rare cases involving MLH1 or MSH6. An autosomal recessive MSI-stable variant has also been described.
Other rare variants include Turcot syndrome (colonic adenomas with central nervous system tumours, mainly MLH1/PMS2 mutations) and constitutional mismatch repair deficiency (CMMRD) (biallelic mutations causing childhood cancers and skin findings mimicking xeroderma pigmentosum).
Who gets Lynch syndrome (epidemiology)?
Lynch syndrome has a worldwide prevalence of ~1:350–1:440, with no significant racial predilection. Lifetime cancer risks vary by gene:
- MLH1/MSH2: Colorectal cancer 40–80%, endometrial 40–60%.
- MSH6: Later onset, endometrial-predominant (up to 70%).
- PMS2: Lowest penetrance (colorectal ~20%).
MTS skin lesions often precede visceral cancers by years, making dermatologic surveillance critical. A systematic review of 961 Lynch syndrome cases identified sebaceous adenomas (43%), sebaceous carcinomas (27%), keratoacanthomas (16%), sebaceomas (13%), squamous cell carcinomas (23%), and basal cell carcinomas (10%) as common cutaneous manifestations. MSH2 variants predominated (72%).
What causes Lynch syndrome?
Lynch syndrome results from heterozygous germline pathogenic variants in MMR genes, leading to defective DNA repair and MSI. Nearly 90% of cases involve MLH1 (30–40%), MSH2 (40–50%), MSH6 (7–10%), or PMS2 (5%). EPCAM deletions cause epigenetic MSH2 silencing (~3%).
Environmental triggers like ultraviolet radiation, radiotherapy, or immunosuppression (e.g., tacrolimus post-transplant) may unmask latent MTS. Unlike sporadic MSI-high cancers driven by MLH1 promoter hypermethylation, Lynch tumours retain one functional MMR allele until loss of heterozygosity occurs.
What are the clinical features of Lynch syndrome?
Lynch syndrome confers high lifetime risks of:
| Cancer Type | Lifetime Risk |
|---|---|
| Colorectal | 40–80% (proximal predominance) |
| Endometrial | 15–60% |
| Ovarian | 8–15% |
| Gastric | 5–10% |
| Urothelial (ureter/renal pelvis) | 1–22% |
| Sebaceous skin tumours (MTS) | ~10% of Lynch cases |
Cutaneous manifestations (predominantly MTS):
- Sebaceous neoplasms: Adenomas (yellow papules), carcinomas (ulcerated nodules), sebaceomas.
- Keratoacanthomas: Multiple, rapid-growing.
- Non-sebaceous: Squamous cell carcinoma (23%), basal cell carcinoma (10%).
Lesions favour trunk/extremities over sun-exposed head/neck. Sebaceous carcinoma recurs locally/metastasises in up to 25%. Internal cancers may behave less aggressively than expected.
How is Lynch syndrome diagnosed?
Clinical criteria: Amsterdam II or Revised Bethesda Guidelines select patients for testing.
Amsterdam II criteria (3/3 required):
- ≥3 relatives with Lynch-associated cancer (one first-degree to the other two).
- ≥2 successive generations.
- ≥1 diagnosed <50 years.
Revised Bethesda (tumour testing triggers):
- Colorectal/endometrial cancer <50 years.
- MSI-high tumours.
- Multiple Lynch cancers.
Diagnostic algorithm:
- IHC for MMR proteins on tumour (loss in 95% Lynch cases).
- MSI testing (90% concordant with IHC).
- Germline sequencing of MMR genes.
For sebaceous tumours: IHC/MSI on skin lesions identifies 95%/90% of underlying genotypes. Solitary sebaceous adenoma <50yo or off head/neck warrants MTS workup.
What is the treatment for Lynch syndrome?
- Cancer prevention: Colonoscopy q1–2 years from 20–25yo; hysterectomy/oophorectomy post-childbearing.
- Chemoprevention: Aspirin 600mg/d reduces colorectal cancer risk.
- Immunosuppressed MTS: Sirolimus preferred.
- Skin lesions: Excision; Mohs for sebaceous carcinoma. Excise keratoacanthoma-like lesions fully.
What is the outlook for Lynch syndrome?
Early detection via surveillance dramatically improves survival. Lynch cancers often have better prognosis than sporadic MSI-high counterparts. Sebaceous carcinoma: 25% recurrence risk requires vigilant follow-up.
Skin surveillance in Lynch syndrome
Annual full skin exams with biopsy of suspicious lesions. Dermatologic surveillance complements cancer screening.
Frequently asked questions
What skin lesions suggest Lynch syndrome?
Sebaceous adenomas/carcinomas, multiple keratoacanthomas, especially <50yo or trunk location.
Should all sebaceous tumours be tested?
Yes if solitary <50yo, multiple, or off head/neck; IHC/MSI guides germline testing.
Does immunosuppression trigger MTS?
Yes, UV/radiotherapy/tacrolimus can unmask latent disease.
Is breast cancer part of Lynch spectrum?
No clear evidence despite some MMR-deficient cases.
References
- Characterization of sebaceous and non-sebaceous cutaneous manifestations in patients with Lynch syndrome: a systematic review — Fam Cancer (Springer). 2022-11-23. https://pubmed.ncbi.nlm.nih.gov/36418753/
- Lynch syndrome (Torre-Muir syndrome) — DermNet NZ. Accessed 2026. https://dermnetnz.org/topics/lynch-syndrome
- Lynch syndrome – Symptoms and causes — Mayo Clinic. 2025-12-02. https://www.mayoclinic.org/diseases-conditions/lynch-syndrome/symptoms-causes/syc-20374714
- Lynch Syndrome and the Skin: A Dermatologist’s Perspective — Dana-Farber Cancer Institute (YouTube). 2024-05-02. https://www.youtube.com/watch?v=0LPn-E_Iqzs
- Dermatology in Lynch Syndrome — Dana-Farber Cancer Institute (YouTube). 2025-05-19. https://www.youtube.com/watch?v=4T-tzw-OoIc
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