Lynch Syndrome - Hereditary Nonpolyposis Colorectal Cancer (HNPCC)

Key Points

Lynch Syndrome (formerly referred to as hereditary nonpolyposis colorectal cancer or HNPCC)

• The presence of microsatellite instability (MSI) helps identify patients at risk for Lynch syndrome (LS); however, it also occurs in ~15% of sporadic colorectal cancers 
• MSI is the accumulation of sequencing errors in microsatellites, or short tandem repeats, which occur during the DNA replication process
• Differentiating colorectal tumors with MSI due to a sporadic somatic event from colorectal tumors with MSI due to a LS germline mutation is important
• LS is an autosomal dominant inherited cancer syndrome that predisposes to colorectal, endometrial, gastric, ovarian, upper urinary tract, and other cancers
• Microsatellite Instability (MSI)

  Microsatellite Instability (MSI)
  Functions as a surrogate marker for defects of mismatch repair (MMR) genes
  Manifests as increases or, more frequently, decreases in the number of  microsatellite* repeats because of defects in MMR genes
  Frequently develops late in tumor development Only 40-50% of adenomatous polyps in LS will have MSI Rare in non-LS polyps Occurs in ~15% of sporadic colorectal cancers 10-15% of LS-associated colorectal carcinomas will have normal MMR protein expression as evaluated by immunohistochemistry staining (IHC)
  Mutation(s) LS Epimutation – monoallelic Sporadic colorectal cancer Epimutation – biallelic Acquired promoter methylation of MLH1
  * Microsatellites are simple repeat sequences of 1-6 base pairs that are repeated up to 100 times and are prone to DNA replication errors.  MMR genes function to identify and correct the replication errors.

  MMR Gene Mutations

  MMR Gene Mutations
  Mutations include point mutations and large genomic deletions or rearrangements
  Common mutations ~90% of mutations in LS	Associated with proximal tumors MLH1 (mutL homolog1) – ~30%  MSH2 (mutS homolog 2) – ~60%
  Less common mutations	PMS2 (postmeiotic segregation increased 2) MSH6 (mutS homolog 6) – often associated with distal tumors and endometrial cancer BRAF V600E (c1779T>A)   Not identified in patients with MLH1 germline mutations Identified in ~15% of sporadic colorectal cancers Highly associated with promoter methylation of MLH1
  Heterodimeric complexes	Obligatory partners MLH1 and PMS2 MLH1 loss leads to concomitant PMS2 loss due to PMS2 degradation MSH2 and MSH6 MSH2 loss leads to concomitant MSH6 loss due to MSH6 degradation MSH6 or PMS2 losses are not associated with any other loss Encoded protein loss associated with constitutive activation of the epidermal growth factor receptor (EGFR) signaling cascade

  Diagnostic Testing for Lynch Syndrome (LS)

  Initial testing* Use immunohistochemistry staining (IHC) or PCR initially to eliminate expense of full gene sequencing. Both tests are sensitive and usually produce concordant results.
  Test		Test Interpretation
  IHC   Uses antibodies to MMR proteins MLH1, MSH2, MSH6, and PMS2 Protein loss identified on IHC will direct mutation testing		IHC Result	Likely Gene Mutation
  		MLH1, PMS2 loss	MLH1
  		MSH2, MSH6 loss	MSH2
  		PMS2	PMS2
  		MSH6	MSH6
  BRAF V600E with hypermethylation for MLH1 IF MLH1 loss is identified with IHC, perform prior to mutation analysis Loss of MLH1 is due to acquired hypermethylation in sporadic tumors, not a germline mutation as in LS ~15% of tumors with MLH1 MSI are sporadic colorectal cancers		If BRAF or MLH1 hypermethylation is positive LS unlikely; most probably sporadic colorectal cancer Gene mutation analysis not necessary unless high suspicion for LS still exists
  PCR (panel of five mononucleotide microsatellites) Relies on detection of microsatellite repeats in the tumor Does not detect specific protein Patient tumor tissue is compared to patient normal tissue Highest sensitivity achieved when PCR is combined with IHC		Determination of MSI
  		High – 2 or more markers with instability Consider gene mutation testing IHC can be used to target specific mutation testing
  		Low (indeterminate) – 1 marker with instability Low risk of LS Consider IHC if high suspicion of LS exists
  		Stable – no markers detected with instability Very low risk of LS Add IHC and possibly gene mutation testing if high suspicion of LS exists
  MOLECULAR ANALYSIS IHC result guides choice of gene to target		Mutation testing is gold standard for diagnosing LS
  *Refer to Lynch Syndrome Testing (HNPCC) algorithm

Diagnosis

Indications for Testing

• Early onset of colorectal cancer or family history of colon cancer in multiple family members
• Women <50 years of age diagnosed with endometrial cancer

Criteria for Diagnosis

• Revised Bethesda guidelines are relevant for identifying colon cancer patients whose tumor should be tested for MSI
  • 90% sensitivity, 80% specificity for Lynch syndrome (LS) and colorectal cancer
• Revised Bethesda guidelines

  Revised Bethesda Guidelines for Testing Colorectal Tumors for Microsatellite Instability (MSI)
  Tumors from individuals should be tested for MSI in the following situations: Colorectal cancera diagnosed in a patient who is <50 years Presence of synchronous, metachronous colorectal, or other HNPCC-associated tumorsb, regardless of age Colorectal cancer with MSI-Hc histologyd diagnosed in a patient who is <60 yearse Colorectal cancer diagnosed in ≥1 first-degree relatives with an HNPCC-related tumor, with one of the cancers being diagnosed at <50 years Colorectal cancer diagnosed in ≥2 first- or second-degree relatives with HNPCC-related tumors, regardless of age
  a Endometrial cancer in women <50 years of age is not included in the revised Bethesda guidelines; however, recent evidence suggests that they should be evaluated for Lynch syndrome b HNPCC-related tumors include colorectal, endometrial, gastric, ovarian, pancreas, ureter and renal pelvis, biliary tract, brain tumors (usually glioblastoma as seen in Turcot syndrome), tumors, sebaceous gland adenomas and keratoacanthomas (as seen in Muir-Torre syndrome), and carcinoma of the small bowel c MSI-H = high MSI in tumors refers to changes in ≥2 of the five National Cancer Institute-recommended panels of microsatellite markers d Presence of tumor infiltrating lymphocytes, Crohn-like lymphocytic reaction, mucinous/signet-ring differentiation, or medullary growth pattern e There was no consensus among the workshop participants on whether to include the age criteria in guideline 3 above; participants voted to keep <60 years of age in the guidelines

• Characteristic features of sporadic colorectal with MSI include the following
  • Absence of family clustering
  • Biallelic methylation of MLH1 promoters
  • Absence of MLH1 and PMS2 proteins on immunohistochemistry
  • Frequent mutation in BRAF
• For additional information regarding testing strategies, refer to the following
  • Key Points tab for this topic
  • Lynch Syndrome Testing (HNPCC) algorithm
  • NCCN guidelines, Colorectal Cancer Screening, page LS-A 2 of 2, for table listing “Tumor Testing Results and Additional Testing Strategies”

Prognosis

• Patients with MSI colorectal cancer have longer survival time than patients without MSI

Differential Diagnosis

• Sporadic colon cancer
• Familial adenomatous polyposis

Screening

Monitoring

Clinical Background

Colon cancer exhibits the characteristics of familial clustering in >10-15% of cases. The most well-characterized hereditary colon cancer is Lynch syndrome (LS – hereditary nonpolyposis colorectal cancer [HNPCC]). LS is caused by a germline mutation in one of the genes within the DNA mismatch repair system. It is the most common cause of hereditary colorectal cancer.

Epidemiology

• Incidence – 1/100,000-1/300,000 in the U.S.
  • Most common hereditary colorectal cancer
• Age – 61 years (mean onset)
  • 70% risk of developing colorectal cancer by age 70 in men
  • 50% risk of developing colorectal cancer by age 70 in women
• Sex – M:F, equal

Inheritance

• Autosomal dominant with incomplete penetrance
• Mutations in 1 of 4 DNA MMR genes
  • MLH1 – 50%
  • MSH2 – 40%
  • MSH6 – 7-10%
  • PMS2 – <5%

Pathophysiology

• LS is associated with accelerated carcinogenesis, causing tiny adenomas to develop into carcinomas within 2-3 years instead of the usual 8-10 years that occurs in sporadic colorectal cancer
• Tumors are more often poorly differentiated with excess mucinous and signet ring cell features
• Microsatellite instability (MSI) is the hallmark of LS but is also present in ~15% of sporadic colorectal cancers
  • MSI is a hypermutable phenotype caused by the loss of DNA MMR activity; also known as the mutation phenotype
• BRAF and MLH1 methylation (sporadic colorectal cancer with MSI)
  • Presence of BRAF V600E mutation or MLH1 promoter methylation in microsatellite unstable tumor indicates that the tumor is probably sporadic, and further workup for LS may not be warranted
  • Lack of BRAF V600E mutation indicates that the tumor may either be sporadic or Lynch-associated

Clinical Presentation

• Early onset of proximal colorectal cancer (often <50 years)
  • Multiple metachronous and synchronous tumors are common
• LS is also associated with early-onset tumors in other organs, including endometrial, ovarian, small bowel, brain, pancreatic, gastric, renal pelvis, ureter

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Carcinoembryonic Antigen 0080080 Method: Quantitative Electrochemiluminescent Immunoassay
Circulating Tumor Cell Count 0093399 Method: Immunomagnetic Separation/Immunofluorescent Stain/Computer Assisted Analysis	May be used to predict survival in patients treated for metastatic breast, prostate, and colorectal cancers May use to evaluate response to therapy
KRAS Mutation Detection with Reflex to BRAF Codon 600 Mutation Detection 2001932 Method: Polymerase Chain Reaction/Pyrosequencing	Determine eligibility for anti-EGFR (cetuximab and panitumumab) therapy in patients with metastatic colorectal cancer
Familial Adenomatous Polyposis Panel: (APC) Sequencing and Deletion/Duplication, (MUTYH) 2 Mutations 2004915 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification	Differential diagnosis of Lynch syndrome

Diagnostic Algorithm

  Lynch Syndrome (HNPCC) Testing Algorithm