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Aim: Microsatellite instability (MSI), which reflects loss of DNA mismatch repair (MMR) activity, and immunohistochemistry (IHC) for MMR proteins are employed as screening examinations for Lynch syndrome (LS). Recent studies revealed that there is a population of MSI‐high tumors in sporadic endometrial cancer (EC). However, MSI data for Japanese EC patients are scarce. Furthermore, sporadic estrogen‐dependent EC (type I) is generally considered to arise from hyperplasia. Because LS is usually associated with type I EC, we hypothesized that MSI might be involved in the oncogenic process in some sporadic EC. We conducted MSI testing to reveal MSI status in sporadic Japanese EC. IHC for MMR proteins was also performed. Methods: Ninety‐eight tissue samples of sporadic ECs from Japanese patients were used for IHC and MSI examinations. We also evaluated MMR protein expressions in the background normal endometrium. Results: Microsatellite instability‐high was observed in 10.2% of 98 cases with sporadic EC, a lower percentage than that in Western studies. Loss of some MMR proteins was observed in 23 cases (23.5%) and there was a significant correlation with MSI‐high status (P < 0.001). Concerning the background endometrium, two cases showed partial loss of MLH1 and PMS2, corresponding to adjacent EC lesions, suggesting that MMR deficiency may already be present in the background endometrium. Conclusion: The MSI‐high rate was low in our Japanese cohort. Our data confirmed the usefulness of MMR protein assessment for MSI screening in Japanese EC patients. Furthermore, IHC of the background endometrium might reveal the mechanism of MSI‐high tumorigenesis. [ABSTRACT FROM AUTHOR]

Background: Lynch syndrome (LS) is the commonest inherited cancer syndrome caused by pathogenic variants of germline DNA mismatch repair (g.MMR) genes. Genome‐wide sequencing is now increasingly applied for tumor characterization, but not for g.MMR. The aim of this study was to evaluate the incidence and pathogenicity of g.MMR variants in Japanese cancer patients. Methods: Four g.MMR genes (MLH1, MSH2, MSH6, and PMS2) were analyzed by next generation sequencing in 1058 cancer patients (614 male, 444 female; mean age 65.6 years) without past diagnosis of LS. The g.MMR variant pathogenicity was classified based on the ClinVar 2015 database. Tumor MMR immunohistochemistry, microsatellite instability (MSI), and BRAF sequencing were also investigated in specific cases. Results: Overall, 46 g.MMR variants were detected in 167 (15.8%) patients, 17 likely benign variants in 119 patients, 24 variants of uncertain significance (VUSs) in 68 patients, two likely pathogenic variants in two patients, and three pathogenic variants in three (0.3%) patients. The three pathogenic variants included two colorectal cancers with MLH1 loss and high MSI and one endometrial cancer with MSH6 loss and microsatellite stability. Two likely pathogenic variants were shifted to VUSs by ClinVar (2018). One colon cancer with a likely benign variant demonstrated MLH1 loss and BRAF mutation, but other nonpathogenic variants showed sustained MMR and microsatellite stability. Conclusions: Universal sequencing of g.MMR genes demonstrated sundry benign variants, but only a small proportion of cancer patients had pathogenic variants. Pathogenicity evaluation using the ClinVar database agreed with MSI, MMR immunohistochemistry, and BRAF sequencing. [ABSTRACT FROM AUTHOR]

As inherited genetic alterations are important etiological factors causing endometrial cancer (EC), our study aimed to outline the ethnic‐related prevalence and the associated clinical and biological characteristics of germline mutations in cancer predisposition genes in Chinese EC patients. One hundred ninety‐eight Chinese EC patients were screened for germline mutations in a panel of cancer susceptibility genes using next‐generation sequencing combined with multiplex ligation‐dependent probe amplification. First, we found that among patients under 50 years of age, 26% (18/69) carried germline genetic mutations, all involving mismatch repair (MMR) genes except for one mutation affecting BRCA1. Second, when we focused on Lynch syndrome (LS) with additional selected patients, 45 were identified to carry pathogenic mutations in MMR genes, with a higher frequency found in MSH2 and MSH6. We found that age at onset, personal and familial history together with immunohistochemical assay results were the most useful criteria for the diagnosis of LS although limitations in routine practice and the sensitivity and specificity of each parameter should be taken into account. One pathogenic mutation in the PALB2 gene was detected in a patient with no breast cancer in her family. Interestingly, we identified a family carrying pathogenic variant in both PMS2 and BRCA1 genes with distinct clinical phenotypes. Multigene panel testing should be recommended to patients based on their clinical information and tumor phenotype. Our study also showed the genetic complexity in EC, which requires further investigations. What's new? Endometrial cancer incidence is increasing in China, presumably owing in part to greater exposure to environmental risk factors such as obesity and hormone therapy. The degree to which hereditary factors influence endometrial cancer burden in Asian populations remains uncertain. Here, screening for germline mutations shows that more than one‐fourth of young Asian endometrial cancer patients carry variants in cancer predisposition genes, primarily mismatch repair (MMR) genes. Most variants affected MMR genes associated with Lynch syndrome. Multigene panel testing further led to the identification of rare mutations in patients with no apparent family history, highlighting a clinical need for mutational screening. [ABSTRACT FROM AUTHOR]

Constitutional mismatch repair (MMR) deficiency (CMMRD) is a rare childhood cancer susceptibility syndrome resulting from biallelic germline loss-of-function mutations in one of the MMR genes. Individuals with CMMRD have high risk to develop a broad spectrum of malignancies and frequently display features reminiscent of neurofibromatosis type 1 (NF1). Evaluation of the clinical findings of genetically proven CMMRD patients shows that not only multiple café-au-lait macules but also any of the diagnostic features of NF1 may be present in a CMMRD patient. This phenotypic overlap may lead to misdiagnosis of CMMRD patients as having NF1, which impedes adequate management of the patients and their families. The spectrum of CMMRD-associated childhood malignancies includes high-grade glioma, acute myeloid leukaemia or rhabdomyosarcoma, also reported as associated with NF1. Reported associations between NF1 and these malignancies are to a large extent based on studies that neither proved the presence of an NF1 germline mutation nor ruled-out CMMRD in the affected. Hence, these associations are challenged by our current knowledge of the phenotypic overlap between NF1 and CMMRD and should be re-evaluated in future studies. Recent advances in the diagnostics of CMMRD should render it possible to definitely state or refute this diagnosis in these individuals. [ABSTRACT FROM AUTHOR]

Germline PMS2 gene mutations were detected by RT- PCR/direct sequencing of total RNA extracted from puromycin-treated peripheral blood lymphocytes ( PBL) and multiplex ligation-dependent probe amplification ( MLPA) analyses of Japanese patients with colorectal cancer ( CRC) fulfilling either the revised Bethesda Guidelines or being an age at disease onset of younger than 70 years, and screened by mismatch repair protein immunohistochemistry of formalin-fixed paraffin embedded sections. Of the 501 subjects examined, 7 (1.40%) showed the downregulated expression of the PMS2 protein alone and were referred to the genetic counseling clinic. Germline PMS2 mutations were detected in 6 (85.7%), including 3 nonsense and 1 frameshift mutations by RT- PCR/direct sequencing and 2 genomic deletions by MLPA. No mutations were identified in the other MMR genes (i.e. MSH2, MLH1 and MSH6). The prevalence of the downregulated expression of the PMS2 protein alone was 1.40% among the subjects examined and IHC results predicted the presence of PMS2 germline mutations. RT- PCR from puromycin-treated PBL and MLPA may be employed as the first screening step to detect PMS2 mutations without pseudogene interference, followed by the long-range PCR/nested PCR validation using genomic DNA. [ABSTRACT FROM AUTHOR]

Hereditary non-polyposis colorectal cancer (HNPCC) is a dominantly inherited cancer predisposition syndrome that is caused by germline mutations in mismatch repair genes. By screening the core promoters of hMSH2, hMLH1, and hMSH6 in 37 Chinese suspected HNPCC families, a novel germline mutation c.−78_−79delGT was found in the hMSH2 promoter. Its pathogenic effects were supported by the following findings: (a) it co-segregated with HNPCC-related cancers and was not present in the 220 control subjects, (b) tumors harboring the mutation lacked the expression of hMSH2 and showed high microsatellite instability, (c) it significantly decreased the promoter activity, and (d) it abolished the binding ability of the transcription factor E1A-F. Loss of heterozygosity (LOH) was found in three of the tumors studied. Intriguingly, in the tumors from patients II:1 and III:1, LOH occurred in the wild-type allele and agreed well with the traditional ‘two-hit’ model. In contrast, in the tumor from patient III:3, LOH occurred in the mutant allele. A pathogenic somatic mutation (c.2210+1G>A) was also found in this tumor; therefore, we proposed that the ‘second hit’ was inactivated by somatic mutation, and the mutant allele was lost during tumor progression; this provided evidence for the new hypothesis for the dual role of LOH. [ABSTRACT FROM AUTHOR]