Best Practice & Research Clinical Gastroenterology 23 (2009) 185–196

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Best Practice & Research ClinicalGastroenterology

5

Genetic testing in gastroenterology: Lynch syndrome

Shilpa Grover, Gastroenterology Clinical Research Fellow a,b, Sapna Syngal,Associate Professor, Harvard Medical School, Director Gastroenterology a,b,*

a Brigham and Women’s Hospital, 75 Francis Street, Boston, MA 02115, USAb Dana-Farber Cancer Institute, 44 Binney Street, Boston, MA 02115, USA

Keywords:Lynch syndromeHereditary non-polyposis colorectal cancerHNPCCmismatch repair genes

* Corresponding author. Tel.: þ1 617 632 5022;E-mail address: ssyngal@partners.org (S. Synga

1521-6918/$ – see front matter � 2009 Elsevier Ltdoi:10.1016/j.bpg.2009.02.006

Lynch syndrome/Hereditary non-polyposis colorectal cancer iscaused by inherited germline mutations in mismatch repair (MMR)genes, and accounts for 2–5% of colorectal cancers (CRC) . It is char-acterized by young onset CRC and an increased risk for gynaecologic,urinary tract and gastrointestinal cancers. Family history evaluationis crucial in the early identification of individuals at risk for Lynchsyndrome. Individuals whose family history includes multiple rela-tives with cancer, two or more primary cancers, or componenttumours diagnosed at a young age, should undergo genetic evalua-tion for Lynch syndrome. Guidelines recommend initial evaluation ofthe tumour with immunohistochemistry or microsatellite instabilitytesting followed by germline testing for mutations in MMR genes inthose with abnormal results. Genetic test results can guide screeningrecommendations for patients and their families. However, resultsare not always conclusive and in such cases recommendations forcancer screening should be individualized on the basis of personaland family history.

� 2009 Elsevier Ltd. All rights reserved.

Background

Lynch syndrome, the most common inherited familial colorectal cancer syndrome results froma mutation in one of the mismatch repair genes MLH1, MSH2, MSH6 and PMS2. Lynch syndromeaccounts for 2-5% of all colorectal cancers (CRC) [1–3]. First described by Warthin [4], the syndromewas recognized in a family with endometrial and colorectal cancer (CRC). Subsequently, the syndromewas broadened to include a spectrum of malignancies when described by Henry Lynch nearly sixdecades later [5–7]. Lynch syndrome is characterized by early onset of CRC and a predisposition to

Fax: þ1 617 632 4088.l).

d. All rights reserved.

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cancers of the endometrium, ovary, stomach, small bowel, urinary tract and brain. Clinically, thedisorder was first defined by the Amsterdam criteria which required the presence of a multigenera-tional family history of CRC and an early age of cancer onset. Subsequently modified, Amsterdam IIcriteria included extraintestinal cancers known to be associated with Lynch syndrome. The Bethesdacriteria and in 2004, the revised Bethesda criteria, were proposed to identify individuals who wouldbenefit from molecular evaluation for Lynch syndrome.

Clinical features of Lynch syndrome

Individuals with Lynch syndrome have an elevated lifetime risk for CRC [8]. In studies that accountfor ascertainment bias, the CRC risk approximates 60–80% [9,10]. Cancer risk varies based on genderand the mismatch repair mutation [8,11–13]. CRCs in Lynch syndrome arise from adenomatous polypsand although individuals with Lynch syndrome develop adenomas more frequently than controls, theydo not present with hundreds to thousands of polyps as seen in classic Familial Adenomatous Polyposis(FAP) [14]. In individuals with Lynch syndrome, a large proportion of adenomas have a villous growthpattern and a high degree of dysplasia [15]. In addition, progression from adenoma to carcinoma mayoccur within 2–3 years, in contrast to 8–10 years in sporadic cases [16,17].

CRC in Lynch syndrome is characterized by an early age of onset. The average age at cancer diagnosisis 45 years, which is nearly two decades earlier than sporadic CRC. Individuals with Lynch syndromeare also at risk for both synchronous (multiple CRCs diagnosed within six months of surgical resectionfor CRC) and metachronous CRC (CRC diagnosed more than six months after surgical resection for CRC)[16]. Colorectal tumours in Lynch syndrome are frequently located in the proximal colon (70%). Unlikesporadic tumours that are anueploid, these CRCs are frequently diploid on flow cytometry and onhistology have an intense Crohn’s-like lymphocytic reaction, a mucinous component or are poorlydifferentiated [18]. Although the underlying mechanism is unclear, CRC in Lynch syndrome has a betterprognosis than sporadic cases [19–22].

Individuals with Lynch syndrome are also at risk for a spectrum of extracolonic malignancies.Endometrial cancer is the second most common malignancy in women. It is estimated that womenwith Lynch syndrome have a 40–60 percent lifetime risk of endometrial cancer and a 10–12 percentlifetime risk of ovarian cancer [10,13,23]. The mean age of diagnosis of endometrial and ovarian canceris approximately ten years earlier than sporadic cases. Ovarian cancer associated with Lynch syndromeis also diagnosed at an earlier stage than sporadic cases, but five-year survival is not significantlydifferent [24].

After colorectal and endometrial cancer, brain tumours are the third leading cause of cancer deathin individuals with Lynch syndrome [25]. Glioblastomas, astrocytomas and oligodendrogliomas of thebrain have been associated with the Turcot variant of Lynch syndrome [26,27] and sebaceousneoplasms of the skin are associated with Muir–Torre syndrome [28]. It is unclear if Lynch syndrome isassociated with an increased risk of cancer of the prostate and breast [29,30], but the spectrum of Lynchassociated malignancies is known to include tumours of the urinary tract, stomach, small intestine andbiliary tract (Table 1).

Genetics of Lynch syndrome

Lynch syndrome follows an autosomal dominant inheritance and over 90% of Lynch syndrome casesare associated with germline mutations in mismatch repair (MMR) genes MLH1 and MSH2 [16].Mutations in MSH6 have been identified in approximately 10% of Lynch syndrome families and in rarecases mutations in PMS2 have been noted.

The MMR system plays an important role in correcting errors that occur during DNA replication.Slippage of DNA occurs frequently during the replication of short mononucleotide or dinucleotiderepeat sequences, also known as microsatellites. This results in too few or too many copies of micro-satellite repeat sequences. Such errors are normally corrected by DNA polymerase, and microsatelliteDNA sequences are rendered stable. For those errors that are not corrected by DNA polymerase, theMMR mechanism acts as the second line of defence.

Table 1Lifetime cancer risk in Lynch syndrome [8–10,13,23,56,76].

Cancer Lifetime Cancer Risk (%)

CRC (Men) 29–62CRC (Women) 19–51Endometrial cancer 40–60Ovarian cancer 3–13Gastric cancer 2–13Urinary tract 1–12Small bowel 4–7Brain 1–4Bile duct/Gall bladder 2

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The MMR system requires the cooperation of genes from the mutS (MSH2, MSH3, MSH6) and mutL(MLH1, MLH3, PMS1, and PMS2) families. MSH2 plays an integral role in this process by recognizing andbinding to the mismatched DNA sequence. Depending on the length of the base-pair mismatch, MSH2forms a heterodimeric complex with MSH6 if a single base-pair mismatch is recognized or with MSH3 ifthere is a larger 2–8 nucleotide insertion or deletion [31,32]. Following this process, a second heter-odimeric complex of MLH1 and PMS2 is then recruited to excise the mismatched nucleotides.

In individuals with Lynch syndrome, due to failure of the MMR mechanism, errors in microsatelliterepeat sequences are not corrected. This phenomenon is referred to as microsatellite instability. Theextent of MMR deficiency and therefore the level of microsatellite instability depends on the geneinvolved. Mutations in MLH1 and MSH2 result in a high level of microsatellite instability. In contrast,MSH6 mutations result in a partial deficiency of MMR function and therefore a low level of micro-satellite instability.

Microsatellite instability does not necessarily result in tumorigenesis as most microsatellite repeatsequences occur in the intron or non-coding area of the genome. In addition, individuals who inherita germline mutation in one mismatch repair gene may have sufficient DNA mismatch repair function.Transformation to malignancy results when the second copy of the affected MMR gene is somaticallymutated (biallelic inactivation) [33,34] and microsatellites are located in the coding regions of genesinvolved in tumour initiation and progression.

Diagnosis of Lynch syndrome

Genetic evaluation for Lynch syndrome serves to confirm the clinical diagnosis of an affectedindividual and in risk stratification of family members. The most widely advocated approach forgenetic evaluation in families without a known mutation is to begin with tumour molecular evaluation.

Tumour molecular evaluation

Microsatellite instability testingAssessment for microsatellite instability (MSI), using DNA extracted from a formalin fixed tumour

block, is most commonly performed with a five-microsatellite marker panel. A panel convened by theU.S. National Cancer Institute has defined the MSI phenotype based on the number of markers thatdemonstrate instability [35]. Tumours are considered MSI high (MSI-H) if two or more of the fivemicrosatellite sequences of the NCI panel are mutated; MSI low (MSI-L) if one microsatellite sequenceis mutated and microsatellite stable (MSS) if none of the five microsatellite sequences in tumour DNAare mutated.

Immunohistochemistry testingImmunohistochemistry (IHC) testing analyses colorectal tumours for the expression of MMR

proteins. Due to defects in MMR genes, tumours in Lynch syndrome frequently reveal loss of stainingfor the antibodies to the mismatch repair proteins MLH1, MSH2, MSH6 and PMS2 [36,37]. Tumour IHCanalysis of carriers of MLH1 mutations demonstrates loss of both MLH1 and PMS2 nuclear staining and

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in MSH2 mutation carriers, there is loss of staining for both MSH2 and MSH6 with normal staining forthe other proteins. In contrast, in tumours of MSH6 and PMS2 mutation carriers there is selective loss ofstaining of only the corresponding protein.

IHC has been proposed as an alternate marker of MMR mutations [38]. Current guidelinesrecommend germline testing for MMR mutations in individuals with abnormal MSI or IHC results.However, both tests have limitations. Although IHC analysis has the distinct advantage of being a fasterand less expensive test, mutations associated with immunoreactive, but non-functional, proteins canresult in false negative IHC results. Several studies have demonstrated slightly lower sensitivity of IHCcompared to MSI testing [39–42]. MSI testing is not without limitations. MSI is only a surrogate markerfor a MMR germline mutation. Although it is present in more than 90% of Lynch-related cancers, up to15% of sporadic CRCs may have MSI abnormalities due to epigenetic mechanisms, i.e. inactivation ofMLH1 by promoter methylation [43]. Therefore, prior to germline testing in tumours with loss of MLH1staining, it has been recommended that BRAF mutation analysis for the p.V600E mutation associatedwith sporadic MLH1 promoter methylation be performed.

Germline testing

Identification of a pathogenic/deleterious germline mutation in one of the four MMR genes iden-tifies individuals with Lynch Syndrome. At risk relatives can then be tested for the identified mutationin the family. If the mutation is found, the individual is identified as being positive for Lynch Syndromeor true positive.

If the identified family mutation is not found, the results are considered true negative. Individualswith true negative results can be excluded from intensive surveillance recommended for patients withLynch syndrome and can be managed as average risk.

In cases where a family history is consistent with Lynch syndrome but there is no identified familymutation or a mutation of unclear pathogenic significance is detected, genetic test results areconsidered indeterminate or uninformative. In such cases, these individuals are still considered athigher than average risk.

Identification of individuals at risk for Lynch syndrome

Clinical criteria

As it is not economically feasible for every patient with CRC to undergo genetic testing for Lynchsyndrome, clinical criteria have been compiled to identify individuals who are likely to be mutationcarriers.

The Amsterdam criteria were proposed in 1991 [19]. However, these criteria were criticized forbeing much too stringent as they required the presence of young onset CRC, in addition to a familyhistory of three CRCs involving two successive generations. The Amsterdam II criteria included otherLynch associated malignancies [44] and therefore had a higher sensitivity of detecting individuals withLynch Syndrome.

With the introduction of molecular diagnostic testing for Lynch Syndrome, the Bethesda criteriawere developed to guide the identification of patients for MSI testing [45]. Studies evaluating theperformance of clinical criteria in populations at high risk for Lynch Syndrome, have demonstrated thatthe Bethesda guidelines have a higher sensitivity compared to the Amsterdam and Amsterdam IIcriteria [46]. The most recent guideline revision, the revised Bethesda criteria, were proposed toimprove the accuracy of identifying patients with Lynch syndrome among unselected CRC patients [47](Table 2).

Two large population-based studies have evaluated the sensitivity of the revised Bethesda criteria indetecting individuals with MMR mutations. The first study, conducted in a Spanish cohort of 1022patients with CRC, demonstrated that the Bethesda and revised Bethesda criteria identified 100% ofpathogenic MMR positive patients [40,48]. In contrast, the second study by Hampel et al noted that ina population-based cohort of 1066 patients with CRC, five of 23 mutation carriers did not meetBethesda and revised Bethesda criteria and would have otherwise been missed [49].

Table 2Revised Bethesda guidelines [47].

Tumours from individuals should be tested for MSI in the following situations:1. CRC diagnosed in a patient who is less than 50 years of age.2. Presence of synchronous, metachronous colorectal, or other HNPCC-associated tumours,a regardless of age.3. CRC with the MSI-Hb histologyc diagnosed in a patient who is less than 60 years of age.4. CRC diagnosed in one or more first-degree relatives with an HNPCC-related tumor, with one of the cancers being diagnosed

under age 50 years.5. CRC diagnosed in two or more first- or second-degree relatives with HNPCC-related tumours, regardless of age.

a Hereditary non-polyposis CRC (HNPCC)-related tumours include colorectal, endometrial, stomach, ovarian, pancreas, ureterand renal pelvis, biliary tract, and brain (usually glioblastoma as seen in Turcot syndrome) tumors, sebaceous gland adenomasand keratoacanthomas in Muir–Torre syndrome, and carcinoma of the small bowel.

b MSI-H¼microsatellite instability high in tumors refers to changes in two or more of the five National Cancer Institute-recommended panels of microsatellite markers.

c Presence of tumor infiltrating lymphocytes, Crohn’s-like lymphocytic reaction, mucinous/signet-ring differentiation, ormedullary growth pattern.

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In light of the limitations in the sensitivity of the revised Bethesda guidelines, an alternativestrategy of universal MSI/IHC testing of all individuals with CRC has been proposed. However, thisstrategy may still fail to identify cases where MMR mutations disrupt MMR function but do not result inMSI, as seen with MSH6 mutations or where IHC results are normal despite a non-functional MMRprotein. Studies are also needed to determine if a strategy of universal molecular evaluation would becost-effective.

Prediction models

Limitations in current clinical strategies have led to the development of prediction models toimprove the identification of individuals with Lynch syndrome and quantify the risk of germline MMRmutations. Three recently published prediction models developed by Barnetson et al [21], thePREMM1,2 model for prediction of MLH1 and MSH2 mutation carriers [50] and the MMRpro [51] areworthy of note.

Barnetson et al analyzed a population-based cohort of 870 CRC patients diagnosed prior to age 55years (derivation cohort). By multivariable regression analysis they developed a two-stage model topredict MLH1, MSH2 and MSH6 mutations. Stage 1 of the model included clinical variables includingpatient age, gender, tumour location, presence of synchronous and metachronous CRCs, family historyof endometrial cancer and CRC and the age of the youngest relative with CRC. Stage 2 of the modelcomprised an analysis of the tumour MSI and IHC results. The model was validated in an independentpopulation of 155 patients with CRC younger than 45 years of age (validation cohort). The modelsensitivity (62%), specificity (97%) and positive predictive value (80%) were superior to the Bethesdaand Amsterdam criteria. The model discrimination, i.e. the ability of the model to separate mutationcarriers from those without a MMR mutation, was similar between the derivation and validationcohort. However, an important model performance measure - model calibration (the degree ofagreement between estimated number of mutation carriers and the actual number of mutationcarriers) was not reported. In addition, the model was developed and validated in a population ofpatients with young onset CRC and did not include Lynch associated cancers other than endometrialcancer.

The PREMM1,2 model (Prediction of mutations in MLH1 and MSH2) was developed in a cohort of1914 individuals at moderate risk for Lynch syndrome who provided a blood sample for genetic testingat a commercial laboratory [50]. The model was developed using clinical data from 898 probands andvalidated in 1016 unrelated probands. The final multivariable logistic regression model included 12variables including proband diagnosis of CRC, colonic adenomas, extracolonic Lynch associated cancersand a family history of Lynch cancers. The PREMM1,2 model showed good discrimination with an areaunder the receiver operating curve of 0.80. Other strengths of the model included its ability toincorporate extracolonic Lynch associated neoplasms and to provide individualized risk predictionusing an easy to use web based interface. The PREMM1,2 model has also been validated in a large

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population-based cohort [52], nonetheless it has some limitations. In its current form, it does notestimate the risk of MSH6 mutations and does not incorporate MSI or IHC results. In addition, it doesnot consider family size or unaffected family members.

The MMRpro model developed by Chen et al estimates the probability of carrying a deleteriousmutation in MLH1, MSH2 and MSH6 genes by translating estimates of mutation prevalence and thepenetrance of MMR genes into mutation predictions based on a Mendelian approach [51]. The modelalso estimates the probability of developing endometrial or CRC in unaffected relatives based onaverages of carriers’ and non-carriers’ risks weighted by carrier probability. In the validation group, theMMRpro model, with or without MSI data, better identified mutation carriers than the Bethesdaguidelines, even though it slightly over predicted the number of carriers. Other strengths of theMMRpro model are its ability to account for family size by including unaffected relatives and toincorporate MSI data. Furthermore, in individuals who have undergone genetic testing and haveindeterminate or uninformative results, the model can provide post-sequencing probability of a dele-terious MMR mutation. These estimates are particularly valuable given that genetic testing has limi-tations in sensitivity and that uninformative results may lead to false reassurance and low adherence toscreening recommendations. Disadvantages of the MMRpro are that it is labour intensive as it requiresentering the entire family pedigree into the program to generate the probability of a mutation.

The development of prediction models raises two important questions. First, how do these modelsperform relative to existing clinical guidelines and relative to one another and second, what is their rolein clinical practise. A recent study by Balmana et al assessed the comparative performance of thePREMM1,2 and the Barnetson models with clinical criteria and with universal molecular screening ina population-based cohort of CRC patients [53]. In this study, 1222 CRC patients underwent tumourtesting with IHC and MSI and those with mismatch repair deficiency underwent germline testing forMLH1/MSH2. Both the Barnetson and PREMM1,2 models had similar AUC (0.92 and 0.93 respectively).The sensitivity of the PREMM1,2 score �5% and the revised Bethesda guidelines was 100% but a Bar-netson score >0.5% missed one mutation carrier (sensitivity of 87%). Because of the lack of availabledata on unaffected family members the performance of the MMRpro model was not assessed in thiscohort.

What is the role of prediction models in clinical practise? The Barnetson and PREMM1,2 modelswere developed for the identification of individuals at risk for Lynch syndrome. Both models have beenshown to have comparable sensitivities to the revised Bethesda criteria. These models can help providequantitative risk assessment and streamline genetic testing by identification of the family memberwith the highest probability of being a mutation carrier. Barnetson et al have suggested that in theclinical setting with the use of readily available data, the model could be used to select a group ofpatients who are candidates for further molecular testing. In the pre-operative setting, a 0.05 cut offcould be used to select tumours for which IHC would be indicated. In such patients if there was lossof IHC, the high positive predictive value of a MMR mutation (80%), would favour a decision for moreextensive surgery rather than a segmental resection. However, before the Barnetson et al model can beused to guide clinical management there is need for additional studies to validate its performance inother cohorts and among individuals with other Lynch associated tumours. The MMRpro, althougha more complex prediction model, has the distinct advantage of being able to incorporate bothmolecular and genetic test results. If used in a specialized setting with genetic counselling it can helpprovide risk estimates to individuals with indeterminate genetic test results.

An approach to genetic evaluation based on current data is outlined in Figs. 1 and 2. Beforeprediction models can be widely incorporated into more advanced medical decision making, externalvalidation studies are needed to assess the transportability of model cut-offs in both population-basedand high risk cohorts.

Management of individuals with Lynch syndrome

The clinical presentation of individuals with Lynch syndrome has been shown to vary based on theMMR mutation. The risk of extracolonic cancers may be higher in families with a MSH2 mutation ascompared to those with a MLH1 mutation [12,54,55]. Families with a MSH6 mutation have an older ageof onset of CRC and have a higher risk of endometrial cancer [56] and patients with mutations in the

Personal and family history meetsrevised Bethesda guidelines

or PREMM1,2 score 5%–19%

Evaluate personal and family historyor compute PREMM1,2 score+$

PREMM1,2 score≥20% or tumor

block not available

MSI or IHC Analysis

Microsatellitestable and IHC

normal

Risk counseling*

Abnormal IHC expressionor microsatellite instability

Germline mutation analysis

PREMM1,2 score<5% or

personal and familyhistory does not meet

revised Bethesdaguidelines

No evaluation indicated

Fig. 1. Algorithm for Genetic Evaluation of Individuals with CRC Based on Bethesda Guidelines and PREMM1,2 scoreþ. þPREMM1,2

score can be computed at the following website http://www.dana-farber.org/pat/cancer/gastrointestinal/crc-calculator/default.asp.$Other models may also be used (each model has own specified cut-offs). Barnetson et al model https://hnpccpredict.hgu.mrc.ac.uk/.MMRpro http://astor.som.jhmi.edu/BayesMendel/[21,51]. *No germline testing. Surveillance recommendations based on personaland family history.

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PMS2 gene have a milder phenotype as compared to those with a MLH1 or MSH2 mutation [57].However, current screening recommendations apply to all individuals with Lynch syndrome, irre-spective of the MMR gene involved. Both the guidelines and the evidence to support them are dis-cussed in this section.

Screening for CRC

Screening for CRC in individuals with Lynch syndrome, has been demonstrated to decrease CRCincidence and mortality [58,59]. In a prospective Finnish screening study that followed individuals overa 15-year period, colonoscopic screening at a three-year interval decreased CRC mortality by 63% [59].

Although there have not been direct comparisons of intervals of cancer screening, several obser-vational studies have reported CRCs in individuals undergoing colonoscopies at three-year intervals. Inone such study of 56 Lynch syndrome families in Finland, 21 CRCs were diagnosed after a previousclean colonoscopy [60]. Half of the cancers diagnosed were within the three-year screening intervaland two were Dukes C at the time of diagnosis.

Current recommendations therefore take into consideration the early age of onset, the predispo-sition for proximal and metachronous cancer, the rapid progression from adenoma to carcinoma andthe incidence of interval cancers. It is therefore recommended that individuals with Lynch syndromeundergo CRC screening with colonoscopy every 1–2 years beginning between the ages of 20–25 years[61,62]. There is currently no upper limit at which it is recommended that screening be discontinued,but above the age of 80 years the risk of CRC is low and the risks of colonoscopy may outweigh thebenefits [63]. In the absence of conclusive data, decisions to discontinue screening should be made onan individual basis.

Likely sporadicCRC,

Risk counseling*

BRAF analysis Microsatellitestable

Tumor IHCanalysis

Abnormal expression Normal expression

Loss of MLH1Tumor MSI

Loss of MSH2, MSH6or PMS2

Microsatelliteinstability

BRAF mutation No BRAF mutation

Risk counseling*Germline mutation analysis

Fig. 2. Potential options for tumour analysis. *No germline testing. Surveillance recommendations based on personal and family history.

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Screening for endometrial cancer

Current consensus guidelines recommend that women at risk for Lynch Syndrome undergoendometrial cancer screening with annual transvaginal ultrasound and endometrial biopsy beginningat 25–35 years of age. Screening for endometrial cancer has not been demonstrated to improve survivalin women with Lynch syndrome but studies have suggested that screening may lead to the detection ofpremalignant lesions or detection of endometrial cancer at an early stage [64].

A study of 41 women enrolled in a program of annual transvaginal ultrasound and CA-125, foundthat 17 of 179 ultrasounds performed were abnormal and required endometrial sampling. Endometrialsampling resulted in the identification of three cases of complex atypia. One interval endometrialcancer was diagnosed by clinical symptoms [65]. In another study of 175 Finnish mutation carriers whounderwent screening with transvaginal ultrasound (TVUS) and intrauterine biopsy every 2–3 years,endometrial cancer was diagnosed in 11 asymptomatic patients. Of these endometrial cancers, eightwere diagnosed by intrauterine biopsies and four endometrial cancers were detected by TVUS [66].Intrauterine sampling also detected 14 additional cases of potentially premalignant hyperplasia.Although the stage at diagnosis and survival tended to be more favourable in the endometrial cancercases detected in the screening group than in symptomatic mutation carriers, these results were notstatistically significant.

An alternative strategy to endometrial cancer screening is prophylactic hysterectomy and bilateralsalpingo-oophorectomy. A retrospective case control study by Schmeler et al examined the occurrenceof endometrial and ovarian cancer in women with Lynch syndrome who had undergone prophylactichysterectomy alone or with bilateral salpingo-oophorectomy, as compared to controls who had notundergone prophylactic surgery [67]. No endometrial cancers occurred in the 61 women whounderwent hysterectomy as compared to 69 endometrial cancers in 210 controls. Additionally, noovarian or peritoneal cancers were diagnosed in the 47 women who had undergone bilateral salpingo-oophorectomy, as compared to 12 of 223 controls.

Although this study supported prophylactic surgery to reduce the risk of endometrial and ovariancancer, it is important to note that the protective effect against ovarian cancer after surgery was not

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statistically significant [68]. In addition, endometrial and ovarian cancers associated with Lynchsyndrome in this and other studies, have been shown to be early stage and curable at the time ofdetection [69,70] with five-year survival rates that are greater than 90 percent [69,71]. Beforeprophylactic surgery can be recommended for all women with Lynch syndrome, prospective cohortstudies assessing the effect of prophylactic surgery on cancer incidence and mortality, as comparedwith gynaecologic screening alone are needed.

Screening for other cancers

As the lifetime risk of gastric cancer and incidence in the U.S and Europe are low, screening forgastric cancer is not routinely recommended. It has been suggested that screening for gastric cancer beperformed if there is clustering of gastric cancers in the family or if there is a high incidence of gastriccancer in the individual’s country of origin. Screening for urothelial cancers in families with clusteringof these tumours by annual urine analysis with cytology and renal ultrasounds starting at 30–35 yearshave also been proposed.

Management of CRC in Lynch syndrome

Individuals with Lynch syndrome are at increased risk of metachronous CRCs. In a Dutch study, thecumulative risk of a second CRC at ten-year follow-up was 15.7% after a partial colectomy as comparedto 3.4% after a subtotal colectomy [72]. Decision analysis has demonstrated a life expectancy gain of 2.3years after subtotal colectomy for primary CRC compared to segmental resection, if performed ata young age (�47 years) [73]. Based on available data and given the risk of metachronous CRC, eval-uation of the entire colon is necessary prior to surgical resection. It is also prudent that the option ofsubtotal colectomy be discussed with patients prior to surgical resection.

Differential diagnosis

In patients with less than a hundred colorectal adenomas, the diagnosis of attenuated familialadenomatous polyposis (AFAP) and MYH associated polyposis (MAP) should be considered. AttenuatedFAP is caused by an inherited mutation in the adenomatous polyposis coli (APC) gene. Unlike patientswith classic FAP who may present with greater than a thousand polyps, patients with AFAP have lessthan a hundred polyps and present in the fourth or fifth decade.

MAP should also be considered in patients with colorectal adenomas/cancer whose family historydoes not indicate vertical transmission. MYH is a base excision repair gene that participates in repair ofoxidative damage. Biallelic mutations in the MYH gene may account for 30% of families with multipleadenomas who do not exhibit an autosomal dominant pattern of inheritance and do not havea pathogenic APC mutation [74]. Genetic testing is necessary to distinguish attenuated FAP and MAPfrom Lynch syndrome and has important implications for medical management.

Summary

Lynch syndrome is the most common hereditary CRC syndrome, but is frequently unrecognized[75]. At this time it is unclear if universal molecular evaluation for all patients with CRC is the mostcost-effective strategy for identification of individuals with Lynch syndrome. However, it is clear thata comprehensive assessment of family cancer history is necessary for the early identification of high-risk individuals so that genetic evaluation can be initiated. There is also strong evidence that screeningcan significantly reduce CRC mortality in individuals with Lynch syndrome. As additional genes areidentified, the interpretation and estimation of cancer risk is likely to become more complex and willnecessitate the utilization of prediction tools to provide reliable and valid estimates of lifetime cancerrisk. Given the complexities in risk assessment, evaluation for Lynch syndrome should be performed ina specialized setting so that risk counselling and recommendations for future screening can be made inpatients with an elevated cancer risk.

Practice points

� Approximately 2–5% of CRCs are caused by germline mutations associated with LynchSyndrome.� Early identification of individuals with Lynch syndrome is essential as these individuals

require intensive cancer surveillance starting at a young age.� Individuals whose family history include multiple individuals with cancer, two or more

primary cancers, or tumours diagnosed at a young age, should undergo genetic evaluation forLynch syndrome.

Research agenda

� Studies are needed to determine the accuracy and cost-effectiveness of universal molecularevaluation in an unselected population of CRC patients.� Evaluation of clinical prediction models in different clinical settings is necessary to ensure the

transportability needed for incorporation into decision making.� Prospective cohort studies are needed to evaluate the efficacy of surveillance and prophy-

lactic surgery.

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