Role of psychological background in cancer susceptibility genetic testing distress: It is not only about a positive result.

Clinical and familial factors predict psychological distress after genetic testing for cancer susceptibility. However, the contribution of an individual's psychological background to such distress is unclear. This study aims to analyze the psychological impact of genetic testing and to identify the profile of individuals at higher risk. This is a longitudinal multicenter study of individuals undergoing genetic testing for cancer susceptibility. Demographic, clinical, genetic, familial, and psychological (personality types, cancer worry) characteristics were assessed by validated questionnaires the day of genetic testing. Distress, uncertainty, and positive experience perception (MICRA scale) were evaluated at the results disclosure visit, and 3 and 12 months afterwards. Multivariate analysis was performed. A total of 714 individuals were included. A high neuroticism score, high baseline cancer worry, and a positive genetic test result were independently associated with higher psychological impact (p-value < 0.05). The highest risk profile (10% of the cohort) included women with high level of neuroticism and a positive result. Uncertainty was mainly associated with a high level of neuroticism, regardless of the genetic test result. A holistic approach to personalized germline genetic counseling should include the assessment of personality dimensions.

Patients' and professionals' perspective of non-in-person visits in hereditary cancer: predictors and impact of the COVID-19 pandemic.

PURPOSE: To identify predictors of patient acceptance of non-in-person cancer genetic visits before and after the COVID-19 pandemic and assess the preferences of health-care professionals. METHODS: Prospective multicenter cohort study (N = 578, 1 February 2018-20 April 2019) and recontacted during the COVID-19 lockdown in April 2020. Health-care professionals participated in May 2020. Association of personality traits and clinical factors with acceptance was assessed with multivariate analysis. RESULTS: Before COVID-19, videoconference was more accepted than telephone-based visits (28% vs. 16% pretest, 30% vs. 19% post-test). Predictors for telephone visits were age (pretest, odds ratio [OR] 10-year increment = 0.79; post-test OR 10Y = 0.78); disclosure of panel testing (OR = 0.60), positive results (OR = 0.52), low conscientiousness group (OR = 2.87), and post-test level of uncertainty (OR = 0.93). Predictors for videoconference were age (pretest, OR 10Y = 0.73; post-test, OR 10Y = 0.75), educational level (pretest: OR = 1.61), low neuroticism (pretest, OR = 1.72), and post-test level of uncertainty (OR = 0.96). Patients' reported acceptance for non-in-person visits after COVID-19 increased to 92% for the pretest and 85% for the post-test. Health-care professionals only preferred non-in-person visits for disclosure of negative results (83%). CONCLUSION: These new delivery models need to recognize challenges associated with age and the psychological characteristics of the population and embrace health-care professionals' preferences.

High-sensitivity microsatellite instability assessment for the detection of mismatch repair defects in normal tissue of biallelic germline mismatch repair mutation carriers.

INTRODUCTION: Lynch syndrome (LS) and constitutional mismatch repair deficiency (CMMRD) are hereditary cancer syndromes associated with mismatch repair (MMR) deficiency. Tumours show microsatellite instability (MSI), also reported at low levels in non-neoplastic tissues. Our aim was to evaluate the performance of high-sensitivity MSI (hs-MSI) assessment for the identification of LS and CMMRD in non-neoplastic tissues. MATERIALS AND METHODS: Blood DNA samples from 131 individuals were grouped into three cohorts: baseline (22 controls), training (11 CMMRD, 48 LS and 15 controls) and validation (18 CMMRD and 18 controls). Custom next generation sequencing panel and bioinformatics pipeline were used to detect insertions and deletions in microsatellite markers. An hs-MSI score was calculated representing the percentage of unstable markers. RESULTS: The hs-MSI score was significantly higher in CMMRD blood samples when compared with controls in the training cohort (p<0.001). This finding was confirmed in the validation set, reaching 100% specificity and sensitivity. Higher hs-MSI scores were detected in biallelic MSH2 carriers (n=5) compared with MSH6 carriers (n=15). The hs-MSI analysis did not detect a difference between LS and control blood samples (p=0.564). CONCLUSIONS: The hs-MSI approach is a valuable tool for CMMRD diagnosis, especially in suspected patients harbouring MMR variants of unknown significance or non-detected biallelic germline mutations.

Comprehensive analysis and ACMG-based classification of CHEK2 variants in hereditary cancer patients.

CHEK2 variants are associated with intermediate breast cancer risk, among other cancers. We aimed to comprehensively describe CHEK2 variants in a Spanish hereditary cancer (HC) cohort and adjust the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG-AMP) guidelines for their classification. First, three CHEK2 frequent variants were screened in a retrospective Hereditary Breast and Ovarian Cancer cohort of 516 patients. After, the whole CHEK2 coding region was analyzed by next-generation sequencing in 1848 prospective patients with HC suspicion. We refined ACMG-AMP criteria and applied different combined rules to classify CHEK2 variants and define risk alleles. We identified 10 CHEK2 null variants, 6 missense variants with discordant interpretation in ClinVar database, and 35 additional variants of unknown significance. Twelve variants were classified as (likely)-pathogenic; two can also be considered "established risk-alleles" and one as "likely risk-allele." The prevalence of (likely)-pathogenic variants in the HC cohort was 0.8% (1.3% in breast cancer patients and 1.0% in hereditary nonpolyposis colorectal cancer patients). Here, we provide ACMG adjustment guidelines to classify CHEK2 variants. We hope that this study would be useful for variant classification of other genes with low effect variants.

Association Between Germline Mutations in BRF1, a Subunit of the RNA Polymerase III Transcription Complex, and Hereditary Colorectal Cancer.

BACKGROUND & AIMS: Although there is a genetic predisposition to colorectal cancer (CRC), few of the genes that affect risk have been identified. We performed whole-exome sequence analysis of individuals in a high-risk family without mutations in genes previously associated with CRC risk to identify variants associated with inherited CRC. METHODS: We collected blood samples from 3 relatives with CRC in Spain (65, 62, and 40 years old at diagnosis) and performed whole-exome sequence analyses. Rare missense, truncating or splice-site variants shared by the 3 relatives were selected. We used targeted pooled DNA amplification followed by next generation sequencing to screen for mutations in candidate genes in 547 additional hereditary and/or early-onset CRC cases (502 additional families). We carried out protein-dependent yeast growth assays and transfection studies in the HT29 human CRC cell line to test the effects of the identified variants. RESULTS: A total of 42 unique or rare (population minor allele frequency below 1%) nonsynonymous genetic variants in 38 genes were shared by all 3 relatives. We selected the BRF1 gene, which encodes an RNA polymerase III transcription initiation factor subunit for further analysis, based on the predicted effect of the identified variant and previous association of BRF1 with cancer. Previously unreported or rare germline variants in BRF1 were identified in 11 of 503 CRC families, a significantly greater proportion than in the control population (34 of 4300). Seven of the identified variants (1 detected in 2 families) affected BRF1 mRNA splicing, protein stability, or expression and/or function. CONCLUSIONS: In an analysis of families with a history of CRC, we associated germline mutations in BRF1 with predisposition to CRC. We associated deleterious BRF1 variants with 1.4% of familial CRC cases, in individuals without mutations in high-penetrance genes previously associated with CRC. Our findings add additional evidence to the link between defects in genes that regulate ribosome synthesis and risk of CRC.

Germline mutations in the spindle assembly checkpoint genes BUB1 and BUB3 are infrequent in familial colorectal cancer and polyposis.

Germline mutations in BUB1 and BUB3 have been reported to increase the risk of developing colorectal cancer (CRC) at young age, in presence of variegated aneuploidy and reminiscent dysmorphic traits of mosaic variegated aneuploidy syndrome. We performed a mutational analysis of BUB1 and BUB3 in 456 uncharacterized mismatch repair-proficient hereditary non-polyposis CRC families and 88 polyposis cases. Four novel or rare germline variants, one splice-site and three missense, were identified in four families. Neither variegated aneuploidy nor dysmorphic traits were observed in carriers. Evident functional effects in the heterozygous form were observed for c.1965-1G>A, but not for c.2296G>A (p.E766K), in spite of the positive co-segregation in the family. BUB1 c.2473C>T (p.P825S) and BUB3 c.77C>T (p.T26I) remained as variants of uncertain significance. As of today, the rarity of functionally relevant mutations identified in familial and/or early onset series does not support the inclusion of BUB1 and BUB3 testing in routine genetic diagnostics of familial CRC.

Elucidating the molecular basis of MSH2-deficient tumors by combined germline and somatic analysis.

In a proportion of patients presenting mismatch repair (MMR)-deficient tumors, no germline MMR mutations are identified, the so-called Lynch-like syndrome (LLS). Recently, MMR-deficient tumors have been associated with germline mutations in POLE and MUTYH or double somatic MMR events. Our aim was to elucidate the molecular basis of MSH2-deficient LS-suspected cases using a comprehensive analysis of colorectal cancer (CRC)-associated genes at germline and somatic level. Fifty-eight probands harboring MSH2-deficient tumors were included. Germline mutational analysis of MSH2 (including EPCAM deletions) and MSH6 was performed. Pathogenicity of MSH2 variants was assessed by RNA analysis and multifactorial likelihood calculations. MSH2 cDNA and methylation of MSH2 and MSH6 promoters were studied. Matched blood and tumor DNA were analyzed using a customized next generation sequencing panel. Thirty-five individuals were carriers of pathogenic or probably pathogenic variants in MSH2 and EPCAM. Five patients harbored 4 different MSH2 variants of unknown significance (VUS) and one had 2 novel MSH6 promoter VUS. Pathogenicity assessment allowed the reclassification of the 4 MSH2 VUS and 6 probably pathogenic variants as pathogenic mutations, enabling a total of 40 LS diagnostics. Predicted pathogenic germline variants in BUB1, SETD2, FAN1 and MUTYH were identified in 5 cases. Three patients had double somatic hits in MSH2 or MSH6, and another 2 had somatic alterations in other MMR genes and/or proofreading polymerases. In conclusion, our comprehensive strategy combining germline and somatic mutational status of CRC-associated genes by means of a subexome panel allows the elucidation of up to 86% of MSH2-deficient suspected LS tumors.

New insights into POLE and POLD1 germline mutations in familial colorectal cancer and polyposis.

Germline mutations in DNA polymerase ɛ (POLE) and δ (POLD1) have been recently identified in families with multiple colorectal adenomas and colorectal cancer (CRC). All reported cases carried POLE c.1270C>G (p.Leu424Val) or POLD1 c.1433G>A (p.Ser478Asn) mutations. Due to the scarcity of cases reported so far, an accurate clinical phenotype has not been defined. We aimed to assess the prevalence of these recurrent mutations in unexplained familial and early-onset CRC and polyposis, and to add additional information to define the clinical characteristics of mutated cases. A total of 858 familial/early onset CRC and polyposis patients were studied: 581 familial and early-onset CRC cases without mismatch repair (MMR) deficiency, 86 cases with MMR deficiency and 191 polyposis cases. Mutation screening was performed by KASPar genotyping assays and/or Sanger sequencing of the involved exons. POLE p.L424V was identified in a 28-year-old polyposis and CRC patient, as a de novo mutation. None of the 858 cases studied carried POLD1 p.S478N. A new mutation, POLD1 c.1421T>C (p.Leu474Pro), was identified in a mismatch repair proficient Amsterdam II family. Its pathogenicity was supported by cosegregation in the family, in silico predictions, and previously published yeast assays. POLE and POLD1 mutations explain a fraction of familial CRC and polyposis. Sequencing the proofreading domains of POLE and POLD1 should be considered in routine genetic diagnostics. Until additional evidence is gathered, POLE and POLD1 genetic testing should not be restricted to polyposis cases, and the presence of de novo mutations, considered.

Germline Mutations in FAN1 Cause Hereditary Colorectal Cancer by Impairing DNA Repair.

Identification of genes associated with hereditary cancers facilitates management of patients with family histories of cancer. We performed exome sequencing of DNA from 3 individuals from a family with colorectal cancer who met the Amsterdam criteria for risk of hereditary nonpolyposis colorectal cancer. These individuals had mismatch repair-proficient tumors and each carried nonsense variant in the FANCD2/FANCI-associated nuclease 1 gene (FAN1), which encodes a nuclease involved in DNA inter-strand cross-link repair. We sequenced FAN1 in 176 additional families with histories of colorectal cancer and performed in vitro functional analyses of the mutant forms of FAN1 identified. We detected FAN1 mutations in approximately 3% of families who met the Amsterdam criteria and had mismatch repair-proficient cancers with no previously associated mutations. These findings link colorectal cancer predisposition to the Fanconi anemia DNA repair pathway, supporting the connection between genome integrity and cancer risk.

POLE and POLD1 mutations in 529 kindred with familial colorectal cancer and/or polyposis: review of reported cases and recommendations for genetic testing and surveillance.

PURPOSE: Germ-line mutations in the exonuclease domains of POLE and POLD1 have been recently associated with polyposis and colorectal cancer (CRC) predisposition. Here, we aimed to gain a better understanding of the phenotypic characteristics of this syndrome to establish specific criteria for POLE and POLD1 mutation screening and to help define the clinical management of mutation carriers. METHODS: The exonuclease domains of POLE and POLD1 were studied in 529 kindred, 441 with familial nonpolyposis CRC and 88 with polyposis, by using pooled DNA amplification and massively parallel sequencing. RESULTS: Seven novel or rare genetic variants were identified. In addition to the POLE p.L424V recurrent mutation in a patient with polyposis, CRC and oligodendroglioma, six novel or rare POLD1 variants (four of them, p.D316H, p.D316G, p.R409W, and p.L474P, with strong evidence for pathogenicity) were identified in nonpolyposis CRC families. Phenotypic data from these and previously reported POLE/POLD1 carriers point to an associated phenotype characterized by attenuated or oligo-adenomatous colorectal polyposis, CRC, and probably brain tumors. In addition, POLD1 mutations predispose to endometrial and breast tumors. CONCLUSION: Our results widen the phenotypic spectrum of the POLE/POLD1-associated syndrome and identify novel pathogenic variants. We propose guidelines for genetic testing and surveillance recommendations.Genet Med 18 4, 325-332.

Cancer Risks Associated With TP53 Pathogenic Variants: Maximum Likelihood Analysis of Extended Pedigrees for Diagnosis of First Cancers Beyond the Li-Fraumeni Syndrome Spectrum.

PURPOSE: Establishing accurate age-related penetrance figures for the broad range of cancer types that occur in individuals harboring a pathogenic germline variant in the TP53 gene is essential to determine the most effective clinical management strategies. These figures also permit optimal use of cosegregation data for classification of TP53 variants of unknown significance. Penetrance estimation can easily be affected by bias from ascertainment criteria, an issue not commonly addressed by previous studies. MATERIALS AND METHODS: We performed a maximum likelihood penetrance estimation using full pedigree data from a multicenter study of 146 TP53-positive families, incorporating adjustment for the effect of ascertainment and population-specific background cancer risks. The analysis included pedigrees from Australia, Spain, and United States, with phenotypic information for 4,028 individuals. RESULTS: Core Li-Fraumeni syndrome (LFS) cancers (breast cancer, adrenocortical carcinoma, brain cancer, osteosarcoma, and soft tissue sarcoma) had the highest hazard ratios of all cancers analyzed in this study. The analysis also detected a significantly increased lifetime risk for a range of cancers not previously formally associated with TP53 pathogenic variant status, including colorectal, gastric, lung, pancreatic, and ovarian cancers. The cumulative risk of any cancer type by age 50 years was 92.4% (95% CI, 82.2 to 98.3) for females and 59.7% (95% CI, 39.9 to 81.3) for males. Females had a 63.3% (95% CI, 35.6 to 90.1) cumulative risk of developing breast cancer by age 50 years. CONCLUSION: The results from maximum likelihood analysis confirm the known high lifetime risk for the core LFS-associated cancer types providing new risk estimates and indicate significantly increased lifetime risks for several additional cancer types. Accurate cancer risk estimates will help refine clinical recommendations for TP53 pathogenic variant carriers and improve TP53 variant classification.

Lessons learnt from the implementation of a colorectal cancer screening programme for lynch syndrome in a tertiary public hospital.

BACKGROUND: Lynch syndrome (LS) is the first cause of inherited colorectal cancer (CRC), being responsible for 2-4% of all diagnoses. Identification of affected individuals is important as they have an increased lifetime risk of multiple CRC and other neoplasms, however, LS is consistently underdiagnosed at the population level. We aimed to evaluate the yield of LS screening in CRC in a single-referral centre and to identify the barriers to its effective implementation. METHODS: LS screening programme included individuals with CRC < 70 years, multiple CRC, or endometrial cancer at any age. Mismatch repair (MMR) protein immunohistochemistry (IHC) analysis was performed in routine practice on the surgical specimen and, if MLH1 IHC was altered, MLH1 gene promoter methylation was analysed. Results were collected in the CRC multidisciplinary board database. LS suspected individuals (altered MMR IHC without MLH1 promoter methylation) were referred to the Cancer Genetic Counselling Unit (CGCU). If accepted, a genetic study was performed. Two checkpoints were included: review of the pathology data and verification of patient referral by a genetic counsellor. RESULTS: Between 2016 and 2019, 381 individuals were included. MMR IHC analysis was performed in 374/381 (98.2 %) CRC cases and MLH1 promoter methylation in 18/21 (85.7 %). Seventeen of the 20 LS suspected individuals were invited for referral at the CGCU. Two cases were not invited and the remaining patient died of cancer before completion of tumour screening. Fifteen individuals attended and a genetic analysis was performed in 15/20 (75 %) LS suspected individuals. Ten individuals were diagnosed with LS, in concordance with the IHC profile (2.7 % of the total cohort). This led to cascade testing in 58/75 (77.3 %) of the available adult relatives at risk, identifying 26 individuals with LS. CONCLUSIONS: Establishing a standardized institutional LS screening programme with checkpoints in the workflow is key to increasing the yield of LS identification.

Evaluation of stress, burnout and hair cortisol levels in health workers at a University Hospital during COVID-19 pandemic.

In the critical context of COVID-19 pandemic, healthcare workers are on the front line, participating directly in the care, diagnosis, and treatment of patients with COVID-19. This exposes them to a higher risk of developing chronic stress, psychological distress, and any other mental health symptoms. OBJECTIVE: to evaluate stress and burnout in a health workers population and, in addition, to measure hair cortisol concentration as a current biomarker of stress. MATERIALS AND METHODS: 234 health workers from Hospital de Clínicas "José de San Martín", Buenos Aires University, were included in this study. In this population hair samples were obtained from the posterior vertex as close to the scalp as possible and the individuals completed the following surveys: perceived stress, social support, burnout scale, life event scale, and sociodemographic data. Hair cortisol was measured by an automated chemiluminescent method. The studied population was divided into three groups considering those individuals below the healthy reference sample range (< 40 pg/mg hair), within the healthy reference range (40-128 pg/mg hair) and above the reference range (> 128 pg/mg hair). This study used a transversal and observational design. RESULTS: Our results show that 40% of the studied population presented hair cortisol values outside of the healthy reference range. In the whole studied population, a direct correlation was found between hair cortisol concentration and perceived stress as well as between hair cortisol concentration and the emotional exhaustion component of burnout (r = 0.142, p = 0.030; r = 0.143, p = 0.029, respectively). 12% of the studied population showed Burnout (52% doctors and residents, 19% nurses, 19% administrative personnel). Higher values in hair cortisol levels were found in the group with burnout versus individuals without burnout (p = 0.034). Finally, a mediation analysis was performed, finding that depersonalization is a mediating variable in the relationship between self-perceived stress and hair cortisol level (F = 4.86, p = 0.0086; indirect effect IC: 0.0987-1.8840). CONCLUSION: This is the first study in which a stress biomarker such as hair cortisol is evaluated in this population and in this context. Healthcare workers are subjected to increased levels of stress and burnout. High depersonalization, emotional exhaustion, and decreased personal sense of accomplishment characterize this population. It is the responsibility of the health authorities to implement strategies to manage this psychological emergency.

Correction: Dueñas et al. Assessing Effectiveness of Colonic and Gynecological Risk Reducing Surgery in Lynch Syndrome Individuals. Cancers 2020, 12, 3419.

In the original article, there was a mistake in Figure 3 as published [...].

Paired Somatic-Germline Testing of 15 Polyposis and Colorectal Cancer-Predisposing Genes Highlights the Role of APC Mosaicism in de Novo Familial Adenomatous Polyposis.

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome responsible for 1% of colorectal cancers (CRCs). Up to 90% of classic FAPs are caused by inactivating mutations in APC, and mosaicism has been previously reported in 20% of de novo cases, usually linked to milder phenotypic manifestations. This study aimed to explore the prevalence of mosaicism in 11 unsolved cases of classic FAP and to evaluate the diagnostic yield of somatic testing. Paired samples of colorectal polyps, tumors, and/or mucosa were analyzed using a custom next-generation sequencing panel targeting 15 polyposis and CRC-predisposing genes. Whenever possible, the extension of mosaicism to blood or sperm was also examined. Of 11 patients with classic adenomatous polyposis, a mosaic pathogenic variant in APC was identified in 7 (64%). No other altered genes were identified. In two of seven patients (29%), mosaicism was found restricted to colonic tissues, whereas in five of seven patients (71%), it was extended to the blood. Germline affectation was confirmed in one patient. We report the first analysis at a somatic level of 15 genes associated with CRC susceptibility, which highlights the role of APC mosaicism in classic FAP etiology. The results further reinforce the importance of testing target tissues when blood test results are negative.

Assessing Effectiveness of Colonic and Gynecological Risk Reducing Surgery in Lynch Syndrome Individuals.

BACKGROUND: Colorectal (CRC) and endometrial cancer (EC) are the most common types of cancer in Lynch syndrome (LS). Risk reducing surgeries (RRS) might impact cancer incidence and mortality. Our objectives were to evaluate cumulative incidences of CRC, gynecological cancer and all-cause mortality after RRS in LS individuals. METHODS: Retrospective analysis of 976 LS carriers from a single-institution registry. Primary endpoints were cumulative incidence at 75 years of cancer (metachronous CRC in 425 individuals; EC and ovarian cancer (OC) in 531 individuals) and all-cause mortality cumulative incidence, comparing extended (ES) vs. segmental surgery (SS) in the CRC cohort and risk reducing gynecological surgery (RRGS) vs. surveillance in the gynecological cohort. RESULTS: Cumulative incidence at 75 years of metachronous CRC was 12.5% vs. 44.7% (p = 0.04) and all-cause mortality cumulative incidence was 38.6% vs. 55.3% (p = 0.31), for ES and SS, respectively. Cumulative, incidence at 75 years was 11.2% vs. 46.3% for EC (p = 0.001) and 0% vs. 12.7% for OC (p N/A) and all-cause mortality cumulative incidence was 0% vs. 52.7% (p N/A), for RRGS vs. surveillance, respectively. CONCLUSIONS: RRS in LS reduces the incidence of metachronous CRC and gynecological neoplasms, also indicating a reduction in all-cause mortality cumulative incidence in females undergoing RRGS.

Comprehensive Constitutional Genetic and Epigenetic Characterization of Lynch-Like Individuals.

The causal mechanism for cancer predisposition in Lynch-like syndrome (LLS) remains unknown. Our aim was to elucidate the constitutional basis of mismatch repair (MMR) deficiency in LLS patients throughout a comprehensive (epi)genetic analysis. One hundred and fifteen LLS patients harboring MMR-deficient tumors and no germline MMR mutations were included. Mutational analysis of 26 colorectal cancer (CRC)-associated genes was performed. Pathogenicity of MMR variants was assessed by splicing and multifactorial likelihood analyses. Genome-wide methylome analysis was performed by the Infinium Human Methylation 450K Bead Chip. The multigene panel analysis revealed the presence of two MMR gene truncating mutations not previously found. Of a total of 15 additional MMR variants identified, five -present in 6 unrelated individuals- were reclassified as pathogenic. In addition, 13 predicted deleterious variants in other CRC-predisposing genes were found in 12 probands. Methylome analysis detected one constitutional MLH1 epimutation, but no additional differentially methylated regions were identified in LLS compared to LS patients or cancer-free individuals. In conclusion, the use of an ad-hoc designed gene panel combined with pathogenicity assessment of variants allowed the identification of deleterious MMR mutations as well as new LLS candidate causal genes. Constitutional epimutations in non-LS-associated genes are not responsible for LLS.

Elucidating the clinical significance of two PMS2 missense variants coexisting in a family fulfilling hereditary cancer criteria.

The clinical spectrum of germline mismatch repair (MMR) gene variants continues increasing, encompassing Lynch syndrome, Constitutional MMR Deficiency (CMMRD), and the recently reported MSH3-associated polyposis. Genetic diagnosis of these hereditary cancer syndromes is often hampered by the presence of variants of unknown significance (VUS) and overlapping phenotypes. Two PMS2 VUS, c.2149G>A (p.V717M) and c.2444C>T (p.S815L), were identified in trans in one individual diagnosed with early-onset colorectal cancer (CRC) who belonged to a family fulfilling clinical criteria for hereditary cancer. Clinico-pathological data, multifactorial likelihood calculations and functional analyses were used to refine their clinical significance. Likelihood analysis based on cosegregation and tumor data classified the c.2444C>T variant as pathogenic, which was supported by impaired MMR activity associated with diminished protein expression in functional assays. Conversely, the c.2149G>A variant displayed MMR proficiency and protein stability. These results, in addition to the conserved PMS2 expression in normal tissues and the absence of germline microsatellite instability (gMSI) in the biallelic carrier ruled out a CMMRD diagnosis. The use of comprehensive strategies, including functional and clinico-pathological information, is mandatory to improve the clinical interpretation of naturally occurring MMR variants. This is critical for appropriate clinical management of cancer syndromes associated to MMR gene mutations.