NCCN Guidelines® Insights: Colorectal Cancer Screening, Version 1.2024.

The NCCN Guidelines for Colorectal Cancer (CRC) Screening describe various colorectal screening modalities as well as recommended screening schedules for patients at average or increased risk of developing sporadic CRC. They are intended to aid physicians with clinical decision-making regarding CRC screening for patients without defined genetic syndromes. These NCCN Guidelines Insights focus on select recent updates to the NCCN Guidelines, including a section on primary and secondary CRC prevention, and provide context for the panel's recommendations regarding the age at which to initiate screening in average-risk individuals and those with increased risk based on personal history of childhood, adolescent, and young adult cancer.

Molecular and Sociodemographic Colorectal Cancer Disparities in Latinos Living in Puerto Rico.

BACKGROUND: The incidence of sporadic colorectal cancer (CRC) among individuals <50 years (early-onset CRC) has been increasing in the United States (U.S.) and Puerto Rico. CRC is currently the leading cause of cancer death among Hispanic men and women living in Puerto Rico (PRH). The objective of this study was to characterize the molecular markers and clinicopathologic features of colorectal tumors from PRH to better understand the molecular pathways leading to CRC in this Hispanic subpopulation. METHODS: Microsatellite instability (MSI), CpG island methylator phenotype (CIMP), and KRAS and BRAF mutation status were analyzed. Sociodemographic and clinicopathological characteristics were evaluated using Chi-squared and Fisher's exact tests. RESULTS: Of the 718 tumors analyzed, 34.2% (n = 245) were early-onset CRC, and 51.7% were males. Among the tumors with molecular data available (n = 192), 3.2% had MSI, 9.7% had BRAF, and 31.9% had KRAS mutations. The most common KRAS mutations observed were G12D (26.6%) and G13D (20.0%); G12C was present in 4.4% of tumors. A higher percentage of Amerindian admixture was significantly associated with early-onset CRC. CONCLUSIONS: The differences observed in the prevalence of the molecular markers among PRH tumors compared to other racial/ethnic groups suggest a distinct molecular carcinogenic pathway among Hispanics. Additional studies are warranted.

Simplified and more sensitive criteria for identifying individuals with pathogenic CDH1 variants.

BACKGROUND: Hereditary diffuse gastric cancer (HDGC) is an autosomal-dominant syndrome most often caused by pathogenic variants in CDH1. The International Gastric Cancer Linkage Consortium (IGCLC) recently updated its criteria for genetic testing. The purpose of this study was to estimate the sensitivity of IGCLC's 2020 criteria for identifying carriers of CDH1 pathogenic variants and to formulate a new set of criteria that is simpler and more sensitive. METHODS: Medical histories of 112 CDH1 mutation carriers, identified predominantly by multigene panel testing, and their 649 family members were reviewed. The percentage of subjects fulfilling the IGCLC 2015 and 2020 criteria was calculated, once without making any assumptions about unavailable pathology, and once assuming gastric cancer to be diffuse when pathology was unavailable. For comparison, we calculated the percentage of subjects who fulfilled our proposed criteria. RESULTS: When making no assumptions about missing pathology, a small (19%) and equal percentage of CDH1 mutation carriers fulfilled the IGCLC 2015 and 2020 criteria. When assuming unspecified gastric cancer to be diffuse, 45 out of 112 (40%) subjects met the 2015 criteria and 53 out of 112 (47%) met the 2020 criteria. Eighty-seven per cent (97/112) fulfilled our proposed criteria. CONCLUSION: In consecutive cases, mostly unselected for clinical criteria of HDGC, the IGCLC 2020 criteria are, at best, marginally more sensitive than previous iterations, but they are also more cumbersome. Unavailable cancer pathology reports are a real-world obstacle to their proper application. Our proposed Yale criteria both address this issue and offer significantly greater sensitivity than the IGCLC 2020 criteria.

Systems approach to enhance Lynch syndrome diagnosis through tumour testing.

BACKGROUND: Guidelines recommend universal mismatch repair (MMR) tumour testing of colorectal adenocarcinomas (CRCs) to screen for Lynch syndrome (LS). However, its implementation remains disjointed and referral for genetic testing dismal, particularly among minorities. We aimed to increase referral, cancer genetic testing and eventually LS diagnosis by developing the CLEAR LS (Closed Loop Enhanced Assessment and Referral for Lynch Syndrome) intervention, a systems approach which in the second phase was automated. METHODS: This is a cohort study of all patients diagnosed with CRC at an academic centre between 1 January 2012, when implementation of universal CRC testing began, and 31 January 2021. The original cohort spanned through 31 May 2015. Tumour testing included MMR immunohistochemistry, followed by BRAF V600E/MLH1 promoter methylation testing when indicated. The intervention included a manual phase (1 June 2015 through 31 July 2018), which systematised pathology screening and cancer genetics (CG) referral mechanisms, and an automated phase (1 August 2018 through 31 January 2021) using computer programming. RESULTS: A total of 249/1541 CRC (17.38%) had MMR loss of expression and 129 (8.37%) qualified for CG evaluation. Referral was 27.58% in the original cohort and 92.1% in the intervention (p<0.001). Patients seen by CG among referred were 27.58% in the original cohort and 74.3% in the intervention (p two-sided<0.001). The distribution of race/ethnicity among patients qualifying and referred for CG evaluation was not significantly different across cohorts. LS diagnosis increased from 0.56% (original cohort) to 1.43% (intervention). Cost per new diagnosis of LS decreased from US$173 675 to $87 960 from original cohort to intervention. CONCLUSION: Implementation of systematic case identification and referral support mechanisms significantly increased the proportion of patients undergoing genetic testing and doubled the percentage of patients diagnosed with LS with no referral differences across racial/ethnic groups.

Mutational signature profiling classifies subtypes of clinically different mismatch-repair-deficient tumours with a differential immunogenic response potential.

BACKGROUND: Mismatch repair (MMR) deficiency is the hallmark of tumours from Lynch syndrome (LS), sporadic MLH1 hypermethylated and Lynch-like syndrome (LLS), but there is a lack of understanding of the variability in their mutational profiles based on clinical phenotypes. The aim of this study was to perform a molecular characterisation to identify novel features that can impact tumour behaviour and clinical management. METHODS: We tested 105 MMR-deficient colorectal cancer tumours (25 LS, 35 LLS and 45 sporadic) for global exome microsatellite instability, cancer mutational signatures, mutational spectrum and neoepitope load. RESULTS: Fifty-three percent of tumours showed high contribution of MMR-deficient mutational signatures, high level of global exome microsatellite instability, loss of MLH1/PMS2 protein expression and included sporadic tumours. Thirty-one percent of tumours showed weaker features of MMR deficiency, 62% lost MSH2/MSH6 expression and included 60% of LS and 44% of LLS tumours. Remarkably, 9% of all tumours lacked global exome microsatellite instability. Lastly, HLA-B07:02 could be triggering the neoantigen presentation in tumours that show the strongest contribution of MMR-deficient tumours. CONCLUSIONS: Next-generation sequencing approaches allow for a granular molecular characterisation of MMR-deficient tumours, which can be essential to properly diagnose and treat patients with these tumours in the setting of personalised medicine.

xDEEP-MSI: Explainable Bias-Rejecting Microsatellite Instability Deep Learning System in Colorectal Cancer.

The prediction of microsatellite instability (MSI) using deep learning (DL) techniques could have significant benefits, including reducing cost and increasing MSI testing of colorectal cancer (CRC) patients. Nonetheless, batch effects or systematic biases are not well characterized in digital histology models and lead to overoptimistic estimates of model performance. Methods to not only palliate but to directly abrogate biases are needed. We present a multiple bias rejecting DL system based on adversarial networks for the prediction of MSI in CRC from tissue microarrays (TMAs), trained and validated in 1788 patients from EPICOLON and HGUA. The system consists of an end-to-end image preprocessing module that tile samples at multiple magnifications and a tissue classification module linked to the bias-rejecting MSI predictor. We detected three biases associated with the learned representations of a baseline model: the project of origin of samples, the patient's spot and the TMA glass where each spot was placed. The system was trained to directly avoid learning the batch effects of those variables. The learned features from the bias-ablated model achieved maximum discriminative power with respect to the task and minimal statistical mean dependence with the biases. The impact of different magnifications, types of tissues and the model performance at tile vs patient level is analyzed. The AUC at tile level, and including all three selected tissues (tumor epithelium, mucin and lymphocytic regions) and 4 magnifications, was 0.87 ± 0.03 and increased to 0.9 ± 0.03 at patient level. To the best of our knowledge, this is the first work that incorporates a multiple bias ablation technique at the DL architecture in digital pathology, and the first using TMAs for the MSI prediction task.

Molecular drivers of tumor progression in microsatellite stable APC mutation-negative colorectal cancers.

The tumor suppressor gene adenomatous polyposis coli (APC) is the initiating mutation in approximately 80% of all colorectal cancers (CRC), underscoring the importance of aberrant regulation of intracellular WNT signaling in CRC development. Recent studies have found that early-onset CRC exhibits an increased proportion of tumors lacking an APC mutation. We set out to identify mechanisms underlying APC mutation-negative (APCmut-) CRCs. We analyzed data from The Cancer Genome Atlas to compare clinical phenotypes, somatic mutations, copy number variations, gene fusions, RNA expression, and DNA methylation profiles between APCmut- and APC mutation-positive (APCmut+) microsatellite stable CRCs. Transcriptionally, APCmut- CRCs clustered into two approximately equal groups. Cluster One was associated with enhanced mitochondrial activation. Cluster Two was strikingly associated with genetic inactivation or decreased RNA expression of the WNT antagonist RNF43, increased expression of the WNT agonist RSPO3, activating mutation of BRAF, or increased methylation and decreased expression of AXIN2. APCmut- CRCs exhibited evidence of increased immune cell infiltration, with significant correlation between M2 macrophages and RSPO3. APCmut- CRCs comprise two groups of tumors characterized by enhanced mitochondrial activation or increased sensitivity to extracellular WNT, suggesting that they could be respectively susceptible to inhibition of these pathways.

NCCN Guidelines® Insights: Genetic/Familial High-Risk Assessment: Colorectal, Version 1.2021.

Identifying individuals with hereditary syndromes allows for timely cancer surveillance, opportunities for risk reduction, and syndrome-specific management. Establishing criteria for hereditary cancer risk assessment allows for the identification of individuals who are carriers of pathogenic genetic variants. The NCCN Guidelines for Genetic/Familial High-Risk Assessment: Colorectal provides recommendations for the assessment and management of patients at risk for or diagnosed with high-risk colorectal cancer syndromes. The NCCN Genetic/Familial High-Risk Assessment: Colorectal panel meets annually to evaluate and update their recommendations based on their clinical expertise and new scientific data. These NCCN Guidelines Insights focus on familial adenomatous polyposis (FAP)/attenuated familial adenomatous polyposis (AFAP) syndrome and considerations for management of duodenal neoplasia.

Analysis of Survival Among Adults With Early-Onset Colorectal Cancer in the National Cancer Database.

Importance: While increased adherence to colorectal cancer (CRC) screening guidelines in the US has been associated with significant reductions in cancer incidence in US individuals aged 50 years and older, the incidence of CRC among those aged younger than 50 years has been steadily increasing. Understanding the survival among individuals with early-onset CRC compared with those aged 50 years and older is fundamental to informing treatment approaches and understanding the unique biological distinctiveness within early-onset CRC. Objective: To characterize the overall survival for individuals with early-onset CRC. Design, Setting, and Participants: This cohort study used data from the National Cancer Database. Included individuals were ages 0 to 90 years and diagnosed with primary CRC from January 1, 2004, through December 31, 2015. Individuals diagnosed at ages 51 through 55 years were selected as the reference group and defined as later-onset CRC for this study. Individuals diagnosed at age 50 years were excluded to minimize an apparent screening detection bias at that age in our population, given that these individuals disproportionately presented with earlier stage. All statistical analyses were conducted from January 4, 2020, through December 26, 2020. Exposures: Early-onset CRC was defined as age younger than 50 years at diagnosis. Main Outcomes and Measures: Overall survival was assessed by Kaplan-Meier analysis and Cox proportional hazards regression. Results: Among 769 871 individuals with CRC (377 890 [49.1%] women; 636 791 White individuals [82.7%]), 353 989 individuals (46.0%) died (median [range] follow-up: 2.9 [0-14.0] years), 102 168 individuals (13.3%) had early-onset CRC, and 78 812 individuals (10.2%) had later-onset CRC. Individuals with early-onset CRC, compared with those diagnosed with CRC at ages 51 through 55 years, had a lower 10-year survival rate (53.6% [95% CI, 53.2%-54.0%] vs 54.3% [95% CI, 53.8%-54.8%]; P < .001) in unadjusted analysis. However, after adjustment for other factors associated with mortality, most notably stage, individuals with early-onset CRC had a lower risk of death compared with individuals diagnosed from ages 51 through 55 years (adjusted hazard ratio [HR], 0.95 [95% CI, 0.93-0.96]; P < .001). In the model adjusted for stage, the HR for individuals with early-onset CRC was 0.89 (95% CI, 0.88-0.90; P < .001). The survival advantage was greatest for individuals diagnosed at ages 35 through 39 years (adjusted HR, 0.88 [95% CI, 0.84-0.92]; P < .001) and stages I (adjusted HR, 0.87 [95% CI, 0.81-0.93]; P < .001) and II (adjusted HR, 0.86 [95% CI, 0.82-0.90]; P < .001) and was absent among those diagnosed at ages 25 years or younger and stages III through IV. Conclusions and Relevance: These findings suggest that there is a survival benefit for individuals with early-onset CRC compared with those diagnosed with CRC at later ages. Further study is needed to understand the underlying heterogeneity of survival among individuals with early-onset CRC by age and stage.

Dickkopf-2 regulates the stem cell marker LGR5 in colorectal cancer via HNF4α1.

Enhanced stemness in colorectal cancer has been reported and it contributes to aggressive progression, but the underlying mechanisms remain unclear. Here we report a Wnt ligand, Dickkopf-2 (DKK2) is essential for developing colorectal cancer stemness. Genetic depletion of DKK2 in intestinal epithelial or stem cells reduced tumorigenesis and expression of the stem cell marker genes including LGR5 in a model of colitis-associated cancer. Sequential mutations in APC, KRAS, TP53, and SMAD4 genes in colonic organoids revealed a significant increase of DKK2 expression by APC knockout and further increased by additional KRAS and TP53 mutations. Moreover, DKK2 activates proto-oncogene tyrosine-protein kinse Src followed by increased LGR5 expressing cells in colorectal cancer through degradation of HNF4α1 protein. These findings suggest that DKK2 is required for colonic epithelial cells to enhance LGR5 expression during the progression of colorectal cancer.

Phenotypic Differences in Juvenile Polyposis Syndrome With or Without a Disease-causing SMAD4/BMPR1A Variant.

Juvenile polyposis syndrome (JPS) is a clinically diagnosed hamartomatous polyposis syndrome that increases the risk of gastrointestinal cancer. Approximately 40%-50% of JPS is caused by a germline disease-causing variant (DCV) in the SMAD4 or BMPR1A genes. The aim of this study was to characterize the phenotype of DCV-negative JPS and compare it with DCV-positive JPS. Herein, we analyzed a cohort of 145 individuals with JPS from nine institutions, including both pediatric and adult centers. Data analyzed included age at diagnosis, family history, cancer history, need for colectomy/gastrectomy, and polyp number and location. Compared with DCV-positive JPS, DCV-negative JPS was associated with younger age at diagnosis (P < 0.001), lower likelihood of having a family history of JPS (P < 0.001), and a lower risk of colectomy (P = 0.032). None of the DCV-negative individuals had gastric or duodenal polyps, and polyp burden decreased after the first decade compared with DCV-positive JPS. Subgroup analysis between SMAD4 and BMPR1A carriers showed that SMAD4 carriers were more likely to have a family history of JPS and required gastrectomy. Taken together, these data provide the largest phenotypic characterization of individuals with DCV-negative JPS to date, showing that this group has distinct differences compared with JPS due to a SMAD4 or BMPR1A variant. Better understanding of phenotype and cancer risk associated with JPS both with and without a DCV may ultimately allow for individualized management of polyposis and cancer risk.Prevention Relevance: Juvenile Polyposis Syndrome (JPS) is a gastrointestinal cancer predisposition syndrome requiring lifelong surveillance, however there is limited data comparing individuals with and without a germline disease-causing variant in SMAD4 or BMPR1A Herein we show that individuals with JPS without an underlying disease-causing variant have distinct phenotypic differences including lack of upper gastrointestinal polyps and lower rates of a family history of JPS, suggesting that a different approach to management may be appropriate in this population.

NCCN Guidelines Insights: Colorectal Cancer Screening, Version 2.2020.

The NCCN Guidelines for Colorectal Cancer (CRC) Screening describe various colorectal screening modalities as well as recommended screening schedules for patients at average or increased risk of developing sporadic CRC. They are intended to aid physicians with clinical decision-making regarding CRC screening for patients without defined genetic syndromes. These NCCN Guidelines Insights focus on select recent updates to the NCCN Guidelines, including a section on primary and secondary CRC prevention, and provide context for the panel's recommendations regarding the age to initiate screening in average risk individuals and follow-up for low-risk adenomas.

AGA White Paper: Roadmap for the Future of Colorectal Cancer Screening in the United States.

The American Gastroenterological Association's Center for Gastrointestinal Innovation and Technology convened a consensus conference in December 2018, entitled, "Colorectal Cancer Screening and Surveillance: Role of Emerging Technology and Innovation to Improve Outcomes." The goal of the conference, which attracted more than 60 experts in screening and related disciplines, including the authors, was to envision a future in which colorectal cancer (CRC) screening and surveillance are optimized, and to identify barriers to achieving that future. This White Paper originates from that meeting and delineates the priorities and steps needed to improve CRC outcomes, with the goal of minimizing CRC morbidity and mortality. A one-size-fits-all approach to CRC screening has not and is unlikely to result in increased screening uptake or desired outcomes owing to barriers stemming from behavioral, cultural, and socioeconomic causes, especially when combined with inefficiencies in deployment of screening technologies. Overcoming these barriers will require the following: efficient utilization of multiple screening modalities to achieve increased uptake; continued development of noninvasive screening tests, with iterative reassessments of how best to integrate new technologies; and improved personal risk assessment to better risk-stratify patients for appropriate screening testing paradigms.

Decreased copy-neutral loss of heterozygosity in African American colorectal cancers.

Despite improvements over the past 20 years, African Americans continue to have the highest incidence and mortality rates of colorectal cancer (CRC) in the United States. While previous studies have found that copy number variations (CNVs) occur at similar frequency in African American and White CRCs, copy-neutral loss of heterozygosity (cnLOH) has not been investigated. In the present study, we used publicly available data from The Cancer Genome Atlas (TCGA) as well as data from an African American CRC cohort, the Chicago Colorectal Cancer Consortium (CCCC), to compare frequencies of CNVs and cnLOH events in CRCs in the two racial groups. Using genotype microarray data, we analyzed large-scale CNV and cnLOH events from 166 microsatellite stable CRCs-31 and 39 African American CRCs from TCGA and the CCCC, respectively, and 96 White CRCs from TCGA. As reported previously, the frequencies of CNVs were similar between African American and White CRCs; however, there was a significantly lower frequency of cnLOH events in African American CRCs compared to White CRCs, even after adjusting for demographic and clinical covariates. Although larger differences for chromosome 18 were observed, a lower frequency of cnLOH events in African American CRCs was observed for nearly all chromosomes. These results suggest that mechanistic differences, including differences in the frequency of cnLOH, could contribute to clinicopathological disparities between African Americans and Whites. Additionally, we observed a previously uncharacterized phenomenon we refer to as small interstitial cnLOH, in which segments of chromosomes from 1 to 5 Mb long were affected by cnLOH.

Genetic Gastric Cancer Risk Syndromes.

PURPOSE OF REVIEW: Gastric cancer is a leading cause of cancer death in the world. Between 1% and 3% of cases are associated with specific genetic cancer risk syndromes. The purpose of this article is to review the latest insights, as well as gaps in knowledge, regarding some of the most common hereditary gastric cancer syndromes: hereditary diffuse gastric cancer (HDGC), gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS), Lynch syndrome, the adenomatous polyposis syndromes, and the hamartomatous polyposis syndromes. RECENT FINDINGS: Patients carrying pathogenic variants in CDH1, but not meeting clinical criteria for HDGC, are increasingly being identified thanks to multigene panel testing; their absence from previous analyses overestimated gastric cancer penetrance. GAPPS is a recently described hereditary gastric cancer syndrome associated with specific point mutations in the promoter 1B region of the APC gene. SUMMARY: Risk of gastric cancer is highest among carriers of pathogenic variants in CDH1, with cumulative incidences approximately 40% and 30% for men and women, respectively. Mutations associated with Lynch syndrome and adenomatous polyposis syndromes confer greatest risk for gastric cancer in East Asian populations. Risk of gastric cancer in GAPPS and hamartomatous polyposis syndromes is difficult to estimate due to their rarity, but mutation status likely determines risk. Future research is needed to more precisely define risk of gastric cancer in these syndromes, so strategies for screening and prophylactic gastrectomy can be optimized.

NCCN Guidelines Insights: Genetic/Familial High-Risk Assessment: Colorectal, Version 2.2019.

Identifying individuals with hereditary syndromes allows for improved cancer surveillance, risk reduction, and optimized management. Establishing criteria for assessment allows for the identification of individuals who are carriers of pathogenic genetic variants. The NCCN Guidelines for Genetic/Familial High-Risk Assessment: Colorectal provide recommendations for the assessment and management of patients with high-risk colorectal cancer syndromes. These NCCN Guidelines Insights focus on criteria for the evaluation of Lynch syndrome and considerations for use of multigene testing in the assessment of hereditary colorectal cancer syndromes.

Scoring colorectal cancer risk with an artificial neural network based on self-reportable personal health data.

Colorectal cancer (CRC) is third in prevalence and mortality among all cancers in the US. Currently, the United States Preventative Services Task Force (USPSTF) recommends anyone ages 50-75 and/or with a family history to be screened for CRC. To improve screening specificity and sensitivity, we have built an artificial neural network (ANN) trained on 12 to 14 categories of personal health data from the National Health Interview Survey (NHIS). Years 1997-2016 of the NHIS contain 583,770 respondents who had never received a diagnosis of any cancer and 1409 who had received a diagnosis of CRC within 4 years of taking the survey. The trained ANN has sensitivity of 0.57 ± 0.03, specificity of 0.89 ± 0.02, positive predictive value of 0.0075 ± 0.0003, negative predictive value of 0.999 ± 0.001, and concordance of 0.80 ± 0.05 per the guidelines of Transparent Reporting of Multivariable Prediction Model for Individual Prognosis or Diagnosis (TRIPOD) level 2a, comparable to current risk-scoring methods. To demonstrate clinical applicability, both USPSTF guidelines and the trained ANN are used to stratify respondents to the 2017 NHIS into low-, medium- and high-risk categories (TRIPOD levels 4 and 2b, respectively). The number of CRC respondents misclassified as low risk is decreased from 35% by screening guidelines to 5% by ANN (in 60 cases). The number of non-CRC respondents misclassified as high risk is decreased from 53% by screening guidelines to 6% by ANN (in 25,457 cases). Our results demonstrate a robustly-tested method of stratifying CRC risk that is non-invasive, cost-effective, and easy to implement publicly.

Clinical features and cancer risk in families with pathogenic CDH1 variants irrespective of clinical criteria.

BACKGROUND: The clinical phenotype of CDH1 pathogenic variant carriers has mostly been studied in families that fulfil criteria of hereditary diffuse gastric cancer (HDGC). We aimed at determining cancer phenotype and cancer risk estimation among families with CDH1 pathogenic variants not selected by HDGC clinical criteria. METHODS: Patients were all consecutively identified CDH1 pathogenic variant carriers from a clinical laboratory tested with multigene panel testing and from an academic cancer genetics programme. Clinical and demographic features, cancer phenotypes and genotype-phenotype correlations were determined among CDH1 families. Age-specific cumulative cancer risks (penetrance) were calculated based on 38 families with available pedigrees. RESULTS: Within the 113 CDH1 pathogenic variant probands and 476 relatives, 113 had gastric cancer, 177 breast cancer and 196 other cancers. Mean age at diagnosis was 47 for gastric and 54 for breast cancer. Forty-six per cent fulfilled criteria of HDGC. While 36% of families had both gastric and breast cancers, 36% had breast but no gastric cancers and 16% had gastric but not breast cancers. Cumulative risk of cancer by age 80 was 37.2% for gastric and 42.9% for breast cancer. CONCLUSION: In unselected CDH1 pathogenic variant carrier families, gastric cancer risks were lower and age at diagnosis higher than previously reported in families pre-selected for HDGC criteria. A substantial proportion of families did not present with any gastric cancers and their cancers were limited to breast. Thus, clinical criteria for CDH1 testing should be widened, including breast cancer families only, and a consideration for delayed prophylactic gastrectomy/surveillance should be evaluated.

Implication of DNA repair genes in Lynch-like syndrome.

Many colorectal cancers (CRCs) that exhibit microsatellite instability (MSI) are not explained by MLH1 promoter methylation or germline mutations in mismatch repair (MMR) genes, which cause Lynch syndrome (LS). Instead, these Lynch-like syndrome (LLS) patients have somatic mutations in MMR genes. However, many of these patients are young and have relatives with cancer, suggesting a hereditary entity. We performed germline sequence analysis in LLS patients and determined their tumor's mutational profiles using FFPE DNA. Six hundred and fifty-four consecutive CRC patients were screened for suspected LS using MSI and absence of MLH1 methylation. Suspected LS cases were exome sequenced to identify germline and somatic mutations. Single nucleotide variants were used to characterize mutational signatures. We identified 23 suspected LS cases. Germline sequence analysis of 16 available samples identified five cases with LS mutations and 11 cases without LS mutations, LLS. Most LLS tumors had a combination of somatic MMR gene mutation and loss of heterozygosity. LLS patients were relatively young and had excess first-degree relatives with cancer. Four of the 11 LLS patients had rare likely pathogenic variants in genes that maintain genome integrity. Moreover, tumors from this group had a distinct mutational signature compared to tumors from LLS patients lacking germline mutations in these genes. In summary, more than a third of the LLS patients studied had germline mutations in genes that maintain genome integrity and their tumors had a distinct mutational signature. The possibility of hereditary factors in LLS warrants further studies so counseling can be properly informed.