The current value of determining the mismatch repair status of ...

Critical Reviews in Oncology/Hematology 116 (2017) 38–57

Contents lists available at ScienceDirect

Critical Reviews in Oncology/Hematology journal homepage: www.elsevier.com/locate/critrevonc

The current value of determining the mismatch repair status of colorectal cancer: A rationale for routine testing E. Ryan a,b , K. Sheahan a,b , B. Creavin a,b , H.M. Mohan a,b , D.C. Winter a,b,∗ a b

Centre for Colorectal Disease, St. Vincent’s University Hospital, Elm Park, Dublin 4, Ireland School of Medicine and Medical Sciences, University College Dublin, Belfield, Dublin 4, Ireland

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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 1.1. Microsatellite instability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 1.2. The mismatch repair gene system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 1.3. Phenotypic differences between MSI and MSS colorectal cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Aetiology of MSI colorectal cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.1. Lynch syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.2. “Lynch-like syndrome” and novel aetiologies of MSI colorectal cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.3. Familial colorectal cancer type X . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.4. Constitutional MMR deficiency syndrome (biallelic constitutional MMR mutations) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.5. Sporadic colorectal cancer with MSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Nomenclature and the determination of the MMR status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1. Diagnosis of MSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2. IHC for dMMR tumours As a surrogate for PCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.3. A comparison of PCR versus IHC for determining MMR status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.4. The role of next generation sequencing In determining MMR status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Significance of MMR status in the algorithm for the diagnosis of lynch syndrome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.1. Age and clinical-based criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.2. Incorporation of BRAF and/or MLH1 promoter hypermethylation assays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 4.3. Universal screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Significance of MSI as a prognostic marker colorectal cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 5.1. MSI As a prognostic marker In colorectal cancer treated with 5-fluorouracil (5-FU) based adjuvant chemotherapy (See Fig. 7) . . . . . . . . . . . . . . 46 5.2. MSI as a prognostic marker with adjuvant 5-FU and irinotecan (FOLFIRI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 5.3. MSI as a prognostic marker with adjuvant 5-FU plus oxaliplatin (FOLFOX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 5.4. MSI as a biomarker with cetuximab adjuvant therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 5.5. MSI as a biomarker with bevacizumab adjuvant therapy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 5.6. The implications of KRAS and BRAF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 5.7. Novel prognostic markers in MSI CRC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Predictive significance of MSI for 5-FU-based chemotherapy (See Fig. 8) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 6.1. Predictive significance of MSI for chemotherapy in stage II/III colorectal cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Predictive significance of MSI for immunotherapy in colorectal cancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 7.1. Predictive significance of MSI for immune checkpoint inhibitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 7.2. The potential for an MSI colorectal cancer vaccine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Notes on rectal cancer, metastatic colorectal cancer and adenomas with MSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 8.1. Rectal cancer with MSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 8.2. Metastatic and recurrent colorectal cancer with MSI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 8.3. Colorectal adenomas with MSI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Conflict of interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Funding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

∗ Corresponding author at: University College Dublin School of Medicine & Medical Sciences, Department of Surgery, St Vincent’s University Hospital, Elm Park, Dublin 4, Ireland. E-mail address: [email protected] (D.C. Winter). http://dx.doi.org/10.1016/j.critrevonc.2017.05.006 1040-8428/© 2017 Elsevier B.V. All rights reserved.

E. Ryan et al. / Critical Reviews in Oncology/Hematology 116 (2017) 38–57

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Research involving human participants and/or animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Informed consent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 Biography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

a r t i c l e

i n f o

Article history: Received 27 October 2016 Received in revised form 2 March 2017 Accepted 15 May 2017 Keywords: Mismatch-repair Microsatellite instability Colorectal cancer Lynch Immunotherapy

a b s t r a c t Colorectal Cancer (CRC) is the third most prevalent cancer in men and women. Up to 15% of CRCs display microsatellite instability (MSI). MSI is reflective of a deficient mismatch repair (MMR) system and is most commonly caused by hypermethylation of the MLH1 promoter. However, it may also be due to autosomal dominant constitutional mutations in DNA MMR, termed Lynch Syndrome. MSI may be diagnosed via polymerase chain reaction (PCR) or alternatively, immunohistochemistry (IHC) can identify MMR deficiency (dMMR). Many institutions now advocate universal tumor screening of CRC via either PCR for MSI or IHC for dMMR to guide Lynch Syndrome testing. The association of sporadic MSI with methylation of the MLH1 promoter and an activating BRAF mutation may offer further exclusion criteria for genetic testing. Aside from screening for Lynch syndrome, MMR testing is important because of its prognostic and therapeutic implications. Several studies have shown MSI CRCs exhibit different clinicopathological features and prognosis compared to microsatellite-stable (MSS) CRCs. For example, response to conventional chemotherapy has been reported to be less in MSI tumours. More recently, MSI tumours have been shown to be responsive to immune-checkpoint inhibition providing a novel therapeutic strategy. This provides a rationale for routine testing for MSI or dMMR in CRC. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Colorectal Cancer (CRC) is the third most prevalent cancer in men and women (Siegel et al., 2012). It accounts for approximately 50,000 deaths each year in the United States (Siegel et al., 2012; Winawer et al., 2003). The reduction in death rates for CRC reflects improvements in earlier cancer detection and management, in combination with an increased understanding of the molecular and genetic basis of the disease (Hagan et al., 2013). It is now apparent that CRC is a heterogeneous disease characterised by a number of molecular subtypes (Guinney et al., 2015). Traditionally two major pathogenetic pathways have been implicated in the development of CRC: the chromosomal instability (CIN) and microsatellite instability (MSI) pathways (Cunningham et al., 2010; Ogino et al., 2011; Shi and Washington, 2012). CIN has recently been subdivided into three further consensus molecular subtypes (CMS), each with distinguishing features: CMS2 (“canonical”), epithelial, marked WNT and MYC signalling activation; CMS3 (“metabolic”), epithelial and evident metabolic dysregulation; and CMS4 (“mesenchymal”), prominent transforming growth factor–␤ activation, stromal invasion and angiogenesis (Guinney et al., 2015). Mismatch repair deficient (dMMR) or MSI tumours, on the other hand, represented in the CMS1 (“microsatellite instability, hypermutated, immune”) subtype, occur when there is deficiency in MMR proteins, generally due to sporadic epigenetic silencing (e.g. by hypermethylation) or by constitutional mutations (e.g. in Lynch syndrome). Diagnosis of MSI is via polymerase chain reaction (PCR) amplification of specific microsatellite repeats. Alternatively, immunohistochemistry (IHC) can confirm the presence or absence of MMR proteins. Sporadic MSI occurs in both CRC and extracolonic malignancies, particularly endometrial cancer (Bruegl et al., 2014; Haraldsdottir et al., 2014). Lynch syndrome (formerly hereditary non-polyposis colorectal cancer [HNPCC]) is the most common heritable cancer predisposition syndrome and is characterised by an increased predisposition to certain cancers, most notably CRC (Vasen et al., 2007). Lynch syndrome tumours are caused by autosomal dominant mutations in the DNA MMR system (Bonadona et al., 2011; Jass, 2007; Kovacs et al., 2009; Lagerstedt Robinson et al., 2007; Ligtenberg et al., 2009; Lynch et al., 2009; van der Klift et al., 2005).

A traditional third or “alternate” molecular CRC pathway, the “serrated pathway”, is characterised by DNA hypermethylation at specific regulatory sites, enriched in CpG motifs (CpG islands) in the promoter regions of tumor suppressor genes (Toyota et al., 1999). There is some overlap between this CpG island methylator phenotype (CIMP) and sporadic MSI cancers due to their association with methylation of the MLH1 promoter and an activating BRAF mutation (Kane et al., 1997). However, BRAF mutation is rare in tumours due to germline deficiency (Lagerstedt Robinson et al., 2007). Thus, BRAF testing or methylation analysis of the MLH1 promoter may offer exclusion criteria for Lynch syndrome genetic testing (EGAPP, 2009). At present there are four major reasons why clinicians may be interested in assessing MSI/MMR status in the CRC patient. 1. The detection of Lynch Syndrome – the role of MMR as a genetic marker of Lynch Syndrome is well established. Both MSI detection and IHC are highly sensitive methods for the identification of a defective MMR system and guide clinicians towards informative, cost-effective genetic testing. These patients benefit from increased surveillance (Jarvinen et al., 2000; Jarvinen et al., 1995), prophylactic aspirin (Burn et al., 2011) and more radical surgery, (Heneghan et al., 2015; Vasen et al., 2013) and may also require different approaches to adjuvant therapy (Le et al., 2015; Sinicrope and Yang, 2011). 2. Prognosis – Several studies have shown dMMR CRC has a better prognosis than MMR proficient (pMMR) CRC (Gavin et al., 2013; Guastadisegni et al., 2010; Klingbiel et al., 2015; Popat et al., 2005; Roth et al., 2010; Sinicrope et al., 2015). MSI tumours are less prone to lymph node (Mohan et al., 2016) and synchronous liver metastasis (Nordholm-Carstensen et al., 2015). However, in metastatic disease MSI seems to confer a negative prognosis. (Goldstein et al., 2014; Mohan et al., 2016; Tran et al., 2011) Grade is not associated with prognosis in dMMR (Mohan et al., 2016; Rosty et al., 2014; Ward et al., 2001). 3. Chemotherapy response – Although with conflicting results, a large amount of preclinical and clinical evidence suggests a possible reduced response to 5-FU based chemotherapy in dMMR tumours (Benatti et al., 2005; Hutchins et al., 2011; Ribic et al.,

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2003; Sargent et al., 2010) According to the National Comprehensive Cancer Network (NCCN), MMR testing should be considered for all patients with stage-II disease, as stage-II MSI tumours have a good prognosis and may not benefit from chemotherapy (NCCN, 2015). 4. Adjuvant Immunomodulatory Therapy – A recent study has shown that advanced stage MSI-associated cancers have better rates of response and progression-free survival (PFS) to the immunomodulatory drug pembrolizumab a monoclonal antibody (MAb) to the immune checkpoint inhibitor Programmed Death 1 (PD-1) when compared to MSS Cancers (Le et al., 2015) and further trials of anti-PD-1 (ClinicalTrials.gov Identifier: NCT02460198) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) therapies (Checkmate 142 [ClinicalTrials.gov Identifier: NCT02060188]) are currently underway. For these reasons increased emphasis has been placed on the importance of determining the MMR status for all newly diagnosed individuals with CRC. Despite this less than half of North American cancer centres routinely perform IHC/PCR to determine the MMR Status of CRC (Beamer et al., 2012). This review describes the aetiology and diagnosis of tumours with MSI and aims to outline how the determination of MMR status is clinically important in the current management of CRC. 1.1. Microsatellite instability Microsatellites are repetitive sequences distributed throughout the genome that consist of nucleotide repeats that are more frequently copied incorrectly when DNA polymerases cannot bind efficiently. MSI is characterised by length alterations within these simple nucleotide tandem repeats in DNA sequences in the patient’s tumor DNA (Ogino and Goel, 2008; Yamamoto and Imai, 2015). The MMR system, consists of several proteins including the products of the MLH1, MSH2, MSH6 and PMS2 genes, and is responsible for the surveillance and correction of such errors. Thus, MSI can be seen as a reflection of a deficient DNA MMR system. This failure to correct errors in DNA replication results in a strong “mutator phenotype” with numerous frameshift mutations in coding and non-coding microsatellites. The DNA slippage within coding sequences may induce frameshift mutations that result in the production of truncated, functionally inactive proteins (Jung et al., 2004; Markowitz et al., 1995; Rampino et al., 1997). The accumulation of mutations in these genes ultimately leads to the development of the MSI, “immune” phenotype due to this high antigenicity (Boland and Goel, 2010; Poulogiannis et al., 2010; Sinicrope, 2010; Vilar and Gruber, 2010; Yamamoto and Imai, 2015). 1.2. The mismatch repair gene system As described above, the MMR system plays a critical role in preserving genetic fidelity (Kunkel and Erie, 2005; Tutlewska et al., 2013). After initial detection of replication errors by the heterodimers MSH2/MSH6 (MutS␣) and MSH2/MSH3 (MutS␤), subsequent recruitment of the MLH1/PMS2 complex degrades the mutated segment and initiates resynthesis of the DNA (Li, 2008). MSH6 expression is normally 10 times that of MSH3, leading to a MutS␣: MutS␤ ratio of about 10:1. Despite the ensuing redundancy in mismatch recognition activities, both complexes are required for pMMR (Peltomaki, 2003). The MMR system is also required for cell cycle arrest and/or programmed cell death in response to certain types of DNA damage (Stojic et al., 2004). Thus, dMMR results in a failure to eliminate severely damaged cells leading to mutagenesis and cancer progression (Kim et al., 2013).

1.3. Phenotypic differences between MSI and MSS colorectal cancer MSI CRC exhibits clinical, pathological, and molecular characteristics that distinguish it from microsatellite stable (MSS) CRC. MSI CRC is most frequently found in the right colon, is associated with; poorly differentiated tumours, a high mucinous component, numerous tumor-infiltrating lymphocytes (TILs), and with the presence of a “Crohn’s-like” host response (Jenkins et al., 2007; Wright and Stewart, 2003). Despite the association of MSI with more advance grade it appears that grade is not associated with prognosis in dMMR (Mohan et al., 2016; Rosty et al., 2014; Ward et al., 2001). 2. Aetiology of MSI colorectal cancer 2.1. Lynch syndrome Lynch Syndrome is the most frequent hereditary CRC syndrome and conservatively accounts for approximately 1–3% of all CRC (Vasen et al., 2007). It is characterised by an increased predisposition to most notably CRC and endometrial cancer, but also gastric cancer, ovarian cancer, hepatobiliary tract cancer, urinary tract cancer, brain cancer and skin cancers, and the cancers often occur at a younger age (See Fig. 1) (Aarnio et al., 1999; Abdel-Rahman et al., 2006; Grover et al., 2009; Hampel et al., 2005; Vasen et al., 2007; Vasen et al., 2001b). This risk varies depending both on the affected MMR gene and on the gene loci involved (Plaschke et al., 2004; ten Broeke et al., 2015; Vasen et al., 2001a; Wijnen et al., 2009). To facilitate genetic counselling and clinical practice, an interactive website providing the complete distributions of all cancer types, depending on gene defect, from any age is now available at is available at http://www.lscarisk.org (Moller et al., 2015). Lynch syndrome is chiefly due to autosomal dominant mutations in the MMR genes MLH1 and MSH2, and less commonly in MSH6 and PMS2 (Aarnio et al., 1999; Bonadona et al., 2011; Gazzoli et al., 2002; Jass, 2007; Koinuma et al., 2004; Lagerstedt Robinson et al., 2007; Lynch et al., 2009; Takemoto et al., 2004). Large genomic rearrangements account for 5–20% of all mutations (Lynch et al., 2009). Germ line hemiallelic methylations of MLH1 or MSH2, termed “epimutations”, have also been recognized as causative of Lynch syndrome (Kloor et al., 2012; Ollila et al., 2006; Sheng et al., 2006). Recently, deletions of the epithelial cell adhesion molecule (EpCAM) gene (previously known as TACSTD1, tumor-associated calcium signal transducer 1), which is located upstream of MSH2, have been implicated in Lynch syndrome (Kovacs et al., 2009; Kuiper et al., 2011; Ligtenberg et al., 2009). Deletions affecting the 3 exons of the EpCAM gene lead to a transcriptional read-through and mediate epigenetic silencing of the MSH2. Therefore, CRCs in individuals with heterozygous constitutional EpCAM deletions will be MSH2-negative MSI cancers (Kovacs et al., 2009; Kuiper et al., 2011; Ligtenberg et al., 2009). It is important to remember that a defect in MMR is not manifest until both alleles of an MMR gene are inactivated (Geiersbach and Samowitz, 2011). A “second hit” on the other allele is required before the defect in MMR becomes evident. Inactivation of the remaining wild type allele can occur by a variety of mechanisms, including deletion, gene conversion, and methylation (Boland and Shike, 2010). When Lynch syndrome is suspected a comprehensive family history should be sought, documenting all diagnoses in 3 generations of the patient’s family (Wattendorf and Hadley, 2005). The American Society of Clinical Oncology (ASCO) has recently recommended a minimum family history set for assessment of cancer risk (See Fig. 2) (Lu et al., 2014). However, in clinical practice detailed family histories can be limited by recall bias, time constraints, an unwillingness to discuss genetic illnesses within families and patients

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41

Lynch Syndrome (MLH1 & MSH2 Only)

Cancer Type

Population Risk

Colon

4.8%

52%-82%

44-61 years

Endometrium

2.7%

25%-60%

48-62 years

Ovary

1.4%

4%-12%

42 years

Stomach