Hereditary Non-Polyposis Colorectal Cancer (Lynch Syndrome)

📋 Key Information Summary

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Lynch syndrome (hereditary non-polyposis colorectal cancer) is an autosomal dominant condition caused by pathogenic germline variants in DNA mismatch repair (MMR) genes — MLH1, MSH2, MSH6, or PMS2 — or EPCAM deletions silencing MSH2.
Accounts for approximately 3–5 % of all colorectal cancers and 2–3 % of endometrial cancers in Australia.
Lifetime colorectal cancer risk is 15–52 % depending on the specific gene affected; MLH1/MSH2 carriers face the highest risk.
Extracolonic cancers include endometrial (up to 60 %), ovarian, gastric, urinary tract, hepatobiliary, small bowel, brain (turcot variant), and sebaceous neoplasms (Muir–Torre variant).
Universal tumour testing — immunohistochemistry (IHC) for MMR protein expression and/or microsatellite instability (MSI) — is recommended for all colorectal and endometrial cancers at diagnosis to identify Lynch syndrome.
The Amsterdam II criteria (clinical) and Bethesda guidelines (tumour-testing trigger) help identify families warranting genetic referral and testing.
Surveillance colonoscopy should commence at age 25 years or 2–5 years before the earliest CRC in the family, whichever is earlier, repeated every 1–2 years.
Surveillance for extracolonic cancers — including upper GI endoscopy, urinalysis, gynaecological screening — is recommended from age 30–35 years.
Aspirin chemoprevention (≥ 300 mg/day for ≥ 2 years) reduces CRC incidence by approximately 35–40 % based on the CAPP2 trial; current NHMRC-endorsed guidance supports consideration of aspirin 100–300 mg daily.
Prophylactic hysterectomy with bilateral salpingo-oophorectomy (BSO) should be discussed with female carriers from age 35–40 years on completion of childbearing.
Lynch-associated colorectal cancers are frequently microsatellite instability–high (MSI-H) and may respond to immune checkpoint inhibitors (pembrolizumab) if metastatic and refractory.
Genetic testing and counselling are available through family cancer clinics across all Australian states and territories, with Telehealth access for remote communities.

Introduction & Australian Epidemiology

Lynch syndrome (LS), historically termed hereditary non-polyposis colorectal cancer (HNPCC), is the most common inherited colorectal cancer predisposition syndrome. It follows an autosomal dominant pattern of inheritance with high penetrance, caused by pathogenic germline variants in the DNA mismatch repair (MMR) genes: MLH1, MSH2, MSH6, and PMS2, as well as deletions in the EPCAM gene that epigenetically silence MSH2.

The MMR system corrects single-nucleotide mismatches and insertion–deletion loops that arise during DNA replication. When MMR function is lost, cells accumulate replication errors — particularly at microsatellite repeat sequences — a phenomenon termed microsatellite instability (MSI). This genomic instability drives tumourigenesis in colorectal epithelium and other tissues.

In Australia, Lynch syndrome is estimated to affect approximately 1 in 280–370 individuals, implying there are roughly 70,000–90,000 carriers nationally. Despite this prevalence, fewer than 5 % of carriers have been identified — the remainder remain undiagnosed and unscreened, representing a significant public health gap.

The Cancer Council Australia and the Australasian Society of Gastrointestinal Pathologists (ASGIP) recommend universal tumour testing — MMR immunohistochemistry (IHC) and/or MSI testing — for every newly diagnosed colorectal and endometrial cancer. This strategy has been shown to be cost-effective in the Australian healthcare setting and is now standard practice in most major cancer centres.

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Clinical pearl: Approximately 75 % of Lynch syndrome carriers who develop CRC have no significant family history fulfilling Amsterdam criteria. Universal tumour testing — not family history alone — is essential for identification.

Parameter	Estimate
Population prevalence	1 in 280–370 individuals
Proportion of all CRC attributable to LS	3–5 %
Proportion of all endometrial cancer	2–3 %
Diagnosed carriers in Australia	< 5 % of total estimated carriers
Median age at CRC diagnosis (untreated)	44–61 years (gene-dependent)

Genetics — MLH1, MSH2, MSH6, PMS2 & EPCAM

Lynch syndrome is caused by monoallelic (heterozygous) pathogenic germline variants in one of four core MMR genes. A somatic "second hit" — typically loss of heterozygosity, promoter methylation, or a second somatic mutation — inactivates the remaining allele and triggers the MMR-deficient phenotype. The specific gene involved determines penetrance, age of onset, and the spectrum of associated cancers.

Gene	Chromosome	Protein	% of LS families	Lifetime CRC risk	Lifetime endometrial risk	Key features
MLH1	3p22.2	MutL homolog 1	~40 %	41–52 %	14–33 %	Highest penetrance; earliest CRC onset; most common in Australian LS families
MSH2	2p21	MutS homolog 2	~34 %	33–52 %	21–60 %	High endometrial risk; Muir–Torre syndrome (sebaceous tumours); associated with EPCAM deletions
MSH6	2p16.3	MutS homolog 6	~18 %	15–33 %	16–44 %	Later-onset CRC; particularly high endometrial cancer risk; may be missed by MSI testing alone
PMS2	7p22.1	PMS1 homolog 2	~8 %	15–20 %	12–15 %	Lowest penetrance; later onset; pseudogene complicate molecular testing; compound heterozygosity causes constitutional MMR deficiency (CMMRD) in childhood
EPCAM deletions	2p21	Epithelial cell adhesion molecule	~1–3 %	Up to 75 % by age 70	Up to 12 %	3′ deletions cause promoter hypermethylation of adjacent MSH2 through transcriptional read-through

Immunohistochemistry Patterns

Loss of nuclear staining on IHC for the respective MMR protein(s) guides targeted germline testing. The characteristic IHC patterns are:

IHC loss pattern	Likely germline gene	Notes
Loss of MLH1 + PMS2	MLH1	Must exclude somatic BRAF V600E mutation or MLH1 promoter hypermethylation (sporadic MSI-H CRC)
Loss of MSH2 + MSH6	MSH2 or EPCAM	Highly specific for LS; proceed directly to MSH2/EPCAM germline testing
Isolated MSH6 loss	MSH6	MSI may be low or stable; rely on IHC rather than MSI panel alone
Isolated PMS2 loss	PMS2	Beware pseudogene interference; specialised long-range PCR or NGS recommended

Constitutional MMR Deficiency (CMMRD)

Biallelic pathogenic variants in MMR genes (most commonly PMS2) cause CMMRD, a severe childhood cancer predisposition syndrome characterised by brain tumours, haematological malignancies, and early-onset CRC. Suspect CMMRD in children with café-au-lait macules, childhood malignancy, and family history suggestive of Lynch syndrome. Diagnosis requires referral to a specialised familial cancer centre.

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Important: All first-degree relatives of an identified MMR gene variant carrier have a 50 % chance of carrying the same variant. Cascade genetic testing should be offered to at-risk relatives as a matter of urgency.

Amsterdam II & Bethesda Criteria

Two sets of clinical criteria help identify individuals and families warranting further investigation for Lynch syndrome. The Amsterdam II criteria are clinical/familial, while the revised Bethesda guidelines indicate which tumours should undergo MMR testing.

Amsterdam II Criteria (1999)

All of the following must be met:

Three or more relatives with an LS-associated cancer (colorectal, endometrial, small bowel, ureter, or renal pelvis)
One affected relative is a first-degree relative of the other two
Two or more successive generations affected
One or more cancers diagnosed before age 50 years
Familial adenomatous polyposis excluded
Tumours verified by histopathology

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Limitation: Amsterdam II criteria have a sensitivity of only ~50–80 % for detecting LS. Many LS carriers have small pedigrees, late-onset disease, or lack the classic multi-generational pattern. Relying solely on family history will miss the majority of carriers.

Revised Bethesda Guidelines (2004)

Tumour testing (MSI or MMR IHC) is recommended for colorectal cancers when any one of the following applies:

CRC diagnosed in a patient aged < 50 years
Synchronous or metachronous LS-associated tumour (colorectal, extracolonic) regardless of age
CRC with MSI-H histology (tumour-infiltrating lymphocytes, Crohn-like reaction, mucinous/signet-ring differentiation, medullary pattern) diagnosed before age 60 years
CRC diagnosed in one or more first-degree relatives with an LS-associated tumour, with one cancer diagnosed before age 50 years
CRC diagnosed in two or more first- or second-degree relatives with LS-associated tumours at any age

Australian Current Practice

The Cancer Council Australia, the Clinical Oncology Society of Australia (COSA), and the Royal College of Pathologists of Australasia (RCPA) now endorse universal tumour testing for all CRC and endometrial cancers regardless of age or family history. This supersedes the age and family-history triggers in the Bethesda guidelines and is supported by cost-effectiveness analyses in the Australian setting.

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Best practice: Universal MMR IHC on all colorectal and endometrial carcinomas at diagnosis. If MLH1/PMS2 lost → perform BRAF V600E and/or MLH1 promoter methylation testing. If methylation/BRAF negative (or other loss pattern) → refer for genetic counselling and germline testing.

Cancer Risks & Surveillance

Lynch syndrome confers elevated lifetime risks of multiple cancer types. The risk magnitude varies by gene. The following table summarises cumulative lifetime risks from pooled cohort studies.

Cancer type	MLH1	MSH2	MSH6	PMS2
Colorectal	41–52 %	33–52 %	15–33 %	15–20 %
Endometrial	14–33 %	21–60 %	16–44 %	12–15 %
Ovarian	4–20 %	8–38 %	~10 %	~3 %
Gastric	~5 %	~5 %	~5 %	~5 %
Urinary tract	~4 %	7–12 %	~2 %	~2 %
Small bowel	~4 %	~6 %	~1 %	~1 %
Brain/CNS	~1 %	~7 %	~1 %	~1 %

Surveillance Protocol

The following surveillance schedule is based on the Cancer Council Australia Clinical Practice Guidelines for Surveillance Colonoscopy, the European Hereditary Tumour Group (EHTG) 2024 guidelines, and the Australian Family Cancer Clinics consensus.

Organ / Test	Commence age	Interval	Notes
Colonoscopy	25 years or 2–5 years before earliest family CRC	Every 1–2 years	If MSH6/PMS2, may consider starting at age 30; annual if prior adenoma or CRC
Upper GI endoscopy + duodenoscopy	30–35 years	Every 3–5 years	More frequent if family history of gastric cancer; consider H. pylori eradication
Urinalysis + urine cytology	30–35 years	Annually	Especially for MSH2 carriers; urine cytology + imaging for haematuria
Gynaecological review ± TVU ± CA-125	30–35 years	Annually	Discuss prophylactic surgery; screening has limited evidence for mortality reduction
Consider abdominal ultrasound	30–35 years	Every 1–2 years	For hepatobiliary and small bowel surveillance in high-risk genotypes
Skin examination	At diagnosis	Annually	Especially for MSH2 — Muir–Torre syndrome (sebaceous gland tumours)

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MBS considerations: Colonoscopy for confirmed Lynch syndrome carriers is claimable under MBS items 32220/32222 (screening/diagnostic colonoscopy in high-risk individuals) when referred by a specialist or with appropriate GP referral and clinical indication. Check current MBS Online for item-specific eligibility and interval rules.

Management & Prophylactic Surgery

Management of Lynch syndrome encompasses cancer prevention (chemoprevention and prophylactic surgery), intensive surveillance, treatment of established cancers, and cascade testing of at-risk relatives.

Aspirin Chemoprevention

The CAPP2 randomised controlled trial demonstrated that aspirin 600 mg daily for at least 2 years reduced CRC incidence by approximately 35–40 % in LS carriers. The CAPP3 trial is ongoing, investigating lower doses (100 mg, 300 mg, 600 mg).

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Aspirin (acetylsalicylic acid)

Aspro Clear® · Cardiprin® · Generic · COX inhibitor / antiplatelet

Adult dose 100–300 mg PO daily (CAPP2 used 600 mg; lower doses under investigation)

Minimum duration ≥ 2 years of continuous use for preventive benefit

Contraindications Active peptic ulcer disease, aspirin-exacerbated respiratory disease, bleeding diathesis, children < 16 years (Reye syndrome risk)

Renal adjustment Use with caution in CKD (eGFR < 30); may impair renal function

PBS status ✔ PBS General Benefit

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Bleeding risk: Aspirin increases risk of GI bleeding. Counsel patients on warning signs (melaena, haematemesis). Consider PPI co-prescription (e.g., esomeprazole 20 mg daily) in patients with additional risk factors (age > 65, concurrent anticoagulants, prior peptic ulcer disease).

Prophylactic Surgery

Prophylactic Gynaecological Surgery

Prophylactic hysterectomy with bilateral salpingo-oophorectomy (BSO) should be discussed with all female LS carriers from age 35–40 years, or on completion of childbearing. This approach eliminates endometrial cancer risk and substantially reduces ovarian cancer risk. There is no reliable screening method for early detection of ovarian cancer in LS.

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Important: Screening for endometrial and ovarian cancer with transvaginal ultrasound and CA-125 has not been shown to reduce mortality. Prophylactic surgery remains the most effective strategy for risk reduction.

Prophylactic Colectomy

Prophylactic total colectomy is not routinely recommended for LS carriers without CRC, given the effectiveness of colonoscopic surveillance and adenoma removal. However, prophylactic (procto-)colectomy may be considered in specific circumstances:

Inability to undergo adequate colonoscopic surveillance
Multiple unresectable flat adenomas or failed endoscopic management
MLH1 or MSH2 carriers with high anxiety about CRC risk after shared decision-making

Treatment of LS-Associated Colorectal Cancer

LS-associated CRCs have distinct biological features that influence treatment:

Stage II CRC: Excellent prognosis (~95 % 5-year survival); 5-fluorouracil (5-FU) adjuvant chemotherapy is NOT recommended as it provides no additional benefit and may cause harm in MMR-deficient stage II tumours.
Stage III CRC: Adjuvant FOLFOX (folinic acid + 5-FU + oxaliplatin) is standard; the survival benefit is similar to sporadic CRC.
Metastatic CRC: MSI-H tumours are highly responsive to immune checkpoint inhibitors. Pembrolizumab (Keynote-177) and nivolumab ± ipilimumab (CheckMate 142) are first-line options for MSI-H/dMMR metastatic CRC.

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Pembrolizumab

Keytruda® · PD-1 inhibitor

Indication First-line treatment of MSI-H/dMMR metastatic CRC

Dose 200 mg IV every 3 weeks or 400 mg IV every 6 weeks

Duration Until disease progression, unacceptable toxicity, or max 2 years

PBS status Authority Required

Cascade Genetic Testing

Once a pathogenic MMR variant is identified in a proband, all first-degree relatives should be offered targeted predictive genetic testing. This is the single most impactful intervention in LS management — identifying carriers before cancer develops enables surveillance and prevention.

In Australia, cascade testing is funded through public familial cancer clinics. Telehealth and postal saliva collection kits are available for geographically remote families.

1

Tumour testing

MMR IHC ± MSI on all CRC and endometrial cancers at diagnosis

2

Exclude sporadic MSI-H

BRAF V600E / MLH1 promoter methylation if MLH1/PMS2 lost

3

Genetic counselling

Refer to family cancer clinic for discussion of germline testing implications

4

Germline testing

Targeted MMR gene panel or comprehensive genomic testing

5

Cascade testing

Predictive testing for at-risk first-degree relatives

6

Surveillance & prevention

Individualised risk-based screening and chemoprevention for confirmed carriers

Special Populations

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Pregnancy

Colonoscopy Safe in the second trimester if clinically indicated; avoid in the first trimester if deferrable

Aspirin Discontinue — teratogenic in first trimester; defer chemoprevention until post-partum

Genetic counselling Offer pre-conception or early pregnancy counselling regarding 50 % inheritance risk; discuss pre-implantation genetic testing (PGT-M) if desired

Delivery No specific obstetric contraindications from LS itself; standard obstetric care

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Paediatrics

Testing age Predictive genetic testing may be offered from age 18 years (or earlier if symptoms arise). Colonoscopy typically starts at 25 years; earlier if symptomatic or CMMRD suspected

CMMRD Biallelic MMR variants — especially PMS2 — require urgent referral to specialised paediatric oncology; surveillance for CNS tumours, haematological malignancies from infancy

Aspirin Contraindicated in children < 16 years (Reye syndrome risk)

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Elderly (> 75 years)

Colonoscopy Risk–benefit of continued surveillance must be individualised; consider comorbidities, life expectancy, and patient preference. May consider lengthening interval or ceasing if limited life expectancy

Aspirin Increased bleeding risk — reassess risk–benefit; consider PPI co-prescription

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Renal Impairment

Aspirin Use with caution if eGFR < 30 mL/min; increased bleeding risk; no dose adjustment required but monitor closely

Pembrolizumab No dose adjustment for renal impairment; monitor for immune-related nephritis

Bowel preparation Polyethylene glycol-based preparations preferred in CKD; avoid phosphate-based preparations (risk of hyperphosphataemia)

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Hepatic Impairment

Aspirin Contraindicated in severe hepatic impairment (Child–Pugh C); increased bleeding risk due to coagulopathy

Pembrolizumab No dose adjustment; monitor for immune-related hepatitis (LFTs every cycle)

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Immunocompromised

Immune checkpoint inhibitors Relative contraindication in active immunosuppressive therapy (e.g., solid organ transplant recipients); discuss with oncology and transplant teams. Surveillance colonoscopy is paramount

Aboriginal & Torres Strait Islander Health Considerations

Aboriginal and Torres Strait Islander Health

Cancer burden

Aboriginal and Torres Strait Islander peoples experience significantly higher colorectal cancer incidence (1.4 times) and mortality compared to non-Indigenous Australians. The AIHW reports that Indigenous Australians are diagnosed at later stages and have lower 5-year survival rates for CRC. Lynch syndrome screening and identification may be particularly impactful in this population given the younger age distribution.

Geographic barriers

Many Indigenous Australians live in remote or very remote communities with limited access to endoscopy services, pathology, and familial cancer clinics. Key actions include: supporting patient travel and accommodation through state/territory Patient Assisted Travel Schemes (PATS); utilising Telehealth for genetic counselling and results disclosure; expanding visiting specialist endoscopy services to remote communities.

Genetic testing access

Uptake of genetic testing among Indigenous Australians is disproportionately low. Barriers include: cultural concerns about blood/ tissue collection, fear of discrimination based on genetic information, distrust of research and health systems, language and health literacy barriers. Solutions: Aboriginal Health Workers (AHWs) as genetic counselling navigators; culturally adapted genetic counselling resources; saliva-based testing alternatives.

Cultural considerations

Kinship systems in Aboriginal and Torres Strait Islander communities mean that genetic diagnoses have broader family implications. Discussions must be culturally safe, involve Elders or family members as appropriate, respect avoidance relationships, and be conducted in language where possible. Consult with local Aboriginal Health Services before initiating cascade testing discussions.

Policy & advocacy

The National Aboriginal Community Controlled Health Organisation (NACCHO) and Cancer Council Australia's National Cancer Prevention Policy support equitable access to cancer genetic services. Funded models integrating AHW-led community education, Telehealth genetic counselling, and mobile endoscopy units have shown improved screening uptake in pilot programmes in the Northern Territory and Far North Queensland.

📚 References

1. Vasen HFA, Mecklin J-P, Khan PM, Lynch HT. The International Collaborative Group on Hereditary Non-Polyposis Colorectal Cancer (ICG-HNPCC). Dis Colon Rectum. 1991;34(5):424–425.
2. Umar A, Boland CR, Terdiman JP, et al. Revised Bethesda Guidelines for hereditary nonpolyposis colorectal cancer (Lynch syndrome) and microsatellite instability. J Natl Cancer Inst. 2004;96(4):261–268.
3. Burn J, Gerdes A-M, Macrae F, et al. Long-term effect of aspirin on cancer risk in carriers of hereditary colorectal cancer: an analysis from the CAPP2 randomised controlled trial. Lancet. 2011;378(9809):2081–2087.
4. Engel C, Ahadova A, Seppälä TT, et al. Associations of pathogenic variants in MLH1, MSH2, and MSH6 with risk of colorectal adenomas and tumors and with somatic mutations in patients with Lynch syndrome. Gastroenterology. 2020;158(5):1326–1333.
5. Cancer Council Australia. Clinical Practice Guidelines for Surveillance Colonoscopy. Sydney: Cancer Council Australia; 2018. Available from: wiki.cancer.org.au.
6. Australian Institute of Health and Welfare (AIHW). Cancer in Aboriginal & Torres Strait Islander people of Australia. Cat. no. CAN 109. Canberra: AIHW; 2018.
7. Royal College of Pathologists of Australasia (RCPA). MMR Immunohistochemistry and Microsatellite Instability Testing for Lynch Syndrome: Quality Assurance Programme. Sydney: RCPA; 2022.
8. Guidelines NG12: Colorectal cancer. National Institute for Health and Care Excellence (NICE). Updated 2020. Available from: nice.org.uk/guidance/ng12.
9. Monahan KJ, Bradshaw N, Dolwani S, et al. Guidelines for the management of hereditary colorectal cancer from the British Society of Gastroenterology (BSG)/Association of Coloproctology of Great Britain and Ireland (ACPGBI)/United Kingdom Cancer Genetics Group (UKCGG). Gut. 2020;69(3):411–444.
10. Stoffel EM, Mangu PB, Gruber SB, et al. Hereditary colorectal cancer syndromes: American Society of Clinical Oncology Clinical Practice Guideline endorsement of the familial risk–colorectal cancer: European Society for Medical Oncology Clinical Practice Guidelines. J Clin Oncol. 2015;33(2):209–217.
11. Biller LH, Syngal S, Yurgelun MB. Recent advances in Lynch syndrome. Fam Cancer. 2019;18(2):211–219.
12. André T, Shiu K-K, Kim TW, et al. Pembrolizumab versus chemotherapy for microsatellite instability–high or mismatch repair–deficient metastatic colorectal cancer (KEYNOTE-177): final analysis of a randomised, open-label, phase 3 study. Lancet Oncol. 2022;23(5):659–670.
13. Crosbie EJ, Ryan NAJ, Arends MJ, et al. The Manchester International Consensus Group recommendations for the management of gynaecological cancers in Lynch syndrome. Genet Med. 2019;21(10):2390–2400.