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Circulating microRNAs (c‐miRs) are small noncoding RNA molecules that migrate throughout the body and regulate gene expression. Global c‐miR expression patterns (c‐miRnomes) change with sporadic carcinogenesis and have predictive potential in early detection of cancers. However, there are no studies that have assessed whether c‐miRnomes display similar potential in carriers of inherited pathogenic mismatch‐repair gene variants (path_MMR), known as Lynch syndrome (LS), who are predisposed to highly increased cancer risk. Using high‐throughput sequencing and bioinformatic approaches, we conducted an exploratory analysis to characterize systemic c‐miRnomes of path_MMR carriers, sporadic rectal cancer patients and non‐LS controls. We showed for the first time that cancer‐free path_MMR carriers have a systemic c‐miRnome of 40 differentially expressed c‐miRs that can distinguish them from non‐LS controls. The systemic c‐miRnome of cancer‐free path_MMR carriers also resembles the systemic c‐miRnomes of cancer patients with or without path_MMR. Our pathway analysis linked the found differentially expressed c‐miRs to carcinogenesis. A total of 508 putative target genes were identified for 32 out of 40 differentially expressed c‐miRs, and 238 of them were enriched in cancer‐related pathways. The most enriched c‐miR‐target genes include well‐known oncogenes and tumor suppressor genes such as BCL2, AKT3, PIK3CA, KRAS, NRAS, CDKN1A and PIK3R1. Taken together, our findings suggest that LS and sporadic carcinogenesis share common biological pathways and alterations in these pathways can produce a c‐miR signature which can track potential oncogenic stress in cancer‐free path_MMR carriers. Therefore, c‐miRs hold potential in monitoring the LS risk stratification patterns during clinical surveillance or cancer management. [ABSTRACT FROM AUTHOR]

Ulcerative colitis increases colorectal cancer risk by mechanisms that remain incompletely understood. We approached this question by determining the genetic and epigenetic profiles of colitis‐associated colorectal carcinomas (CA‐CRC). The findings were compared to Lynch syndrome (LS), a different form of cancer predisposition that shares the importance of immunological factors in tumorigenesis. CA‐CRCs (n = 27) were investigated for microsatellite instability, CpG island methylator phenotype and somatic mutations of 999 cancer‐relevant genes ("Pan‐cancer" panel). A subpanel of "Pan‐cancer" design (578 genes) was used for LS colorectal tumors (n = 28). Mutational loads and signatures stratified CA‐CRCs into three subgroups: hypermutated microsatellite‐unstable (Group 1, n = 1), hypermutated microsatellite‐stable (Group 2, n = 9) and nonhypermutated microsatellite‐stable (Group 3, n = 17). The Group 1 tumor was the only one with MLH1 promoter hypermethylation and exhibited the mismatch repair deficiency‐associated Signatures 21 and 15. Signatures 30 and 32 characterized Group 2, whereas no prominent single signature existed in Group 3. TP53, the most common mutational target in CA‐CRC (16/27, 59%), was similarly affected in Groups 2 and 3, but DNA repair genes and Wnt signaling genes were mutated significantly more often in Group 2. In LS tumors, the degree of hypermutability exceeded that of the hypermutated CA‐CRC Groups 1 and 2, and somatic mutational profiles and signatures were different. In conclusion, Groups 1 (4%) and 3 (63%) comply with published studies, whereas Group 2 (33%) is novel. The existence of molecularly distinct subgroups within CA‐CRC may guide clinical management, such as therapy options. What's new? Ulcerative colitis‐associated colorectal carcinoma (CA‐CRC) is a complex disease involving inflammation‐associated tumorigenesis and genetic mutation. Despite extensive knowledge of germline defects linked to CA‐CRC, however, molecular pathogenesis of the disease remains poorly defined. In this study, using tumor profiling, the authors describe three genetic and epigenetic CA‐CRC subgroups, two of which are previously known and one that is novel. The novel subgroup consisted of hypermutated microsatellite‐stable tumors, which displayed distinct mutational signatures compared to the remaining CA‐CRC subgroups and Lynch syndrome tumors, suggesting pathophysiologic differences. The existence of molecular subgroups within CA‐CRCs may inform treatment decisions. [ABSTRACT FROM AUTHOR]

Background: Lifetime incidence of colorectal cancer (CRC) especially in carriers of MLH1 and MSH2 pathogenic germline variants in mismatch repair genes is high despite ongoing colonoscopy surveillance. Lynch syndrome (LS) registries have been criticized for not reporting colonoscopy quality adequately. Methods: Prospective follow-up data from the national registry were combined with a retrospective assessment of the colonoscopy reports from Helsinki University Hospital electronic patients records in 2004–2019. Results: Total of 366 MLH1, MSH2 and MSH6 carriers underwent 1564 colorectal endoscopies (mean 4.3 per patient, range 1–10) at a single unit. At least one subsequent examination was performed on 336 patients. Bowel preparation was suboptimal (Boston Bowel Preparation Scale 0–2) on either right or left side of the colon in 12.9% of planned surveillance examinations. Caecal intubation rate for full-length colonoscopies was 98.9%. Adenoma detection rate (ADR) was 15.8% in 2004–2014 but substantially increased (21.9%) after introduction of high-definition (HD) technology in 2015–2019 (p =.004; 18.7% across all examinations). CRCs were detected in 23 cases. Nineteen cancers were detected after 977 optimal quality colonoscopies and 4 after 151 compromised quality (BBPS <3 or non-complete examination; p =.16). Advanced neoplasias were not more frequently reported after compromised quality examinations. Conclusion: The majority of LS-associated incident CRCs were detected after colonoscopies with proper bowel preparation and complete examination. There is a considerable time trend towards higher ADR after introducing HD technology of endoscopes. The effect of time trend in ADR to CRC incidence in LS needs to be studied in larger, prospective settings. [ABSTRACT FROM AUTHOR]

Immunological and epigenetic changes are interconnected and contribute to tumorigenesis. We determined the immunoprofiles and promoter methylation of inflammation-related genes for colitis-associated colorectal carcinomas (CA-CRC). The results were compared with Lynch syndrome (LS)-associated colorectal tumors, which are characterized by an active immune environment through inherited mismatch repair defects. CA-CRCs (n = 31) were immunohistochemically evaluated for immune cell scores (ICSs) and PDCD1 and CD274 expression. Seven inflammation-associated genes (CD274, NTSR1, PPARG, PTGS2, PYCARD, SOCS1, and SOCS2), the repair gene MGMT, and eight standard marker genes for the CpG Island Methylator Phenotype (CIMP) were investigated for promoter methylation in CA-CRCs, LS tumors (n = 29), and paired normal mucosae by multiplex ligation-dependent probe amplification. All but one CA-CRCs were microsatellite-stable and all LS tumors were microsatellite-unstable. Most CA-CRCs had a high ICS (55%) and a positive CD274 expression in immune cells (52%). NTSR1 revealed frequent tumor-specific hypermethylation in CA-CRC and LS. When compared to LS mucosae, normal mucosae from patients with CA-CRC showed significantly higher methylation of NTSR1 and most CIMP markers. In conclusion, CA-CRCs share a frequent ICShigh/CD274pos expression pattern with LS tumors. Elevated methylation in normal mucosa may indicate field cancerization as a feature of CA-CRC-associated tumorigenesis. [ABSTRACT FROM AUTHOR]

Regular colonoscopy even with short intervals does not prevent all colorectal cancers (CRC) in Lynch syndrome (LS). In the present study, we asked whether cancers detected under regular colonoscopy surveillance (incident cancers) are phenotypically different from cancers detected at first colonoscopy (prevalent cancers). We analyzed clinical, histological, immunological and mutational characteristics, including panel sequencing and high-throughput coding microsatellite (cMS) analysis, in 28 incident and 67 prevalent LS CRCs (n total = 95). Incident cancers presented with lower UICC and T stage compared to prevalent cancers (p < 0.0005). The majority of incident cancers (21/28) were detected after previous colonoscopy without any pathological findings. On the molecular level, incident cancers presented with a significantly lower KRAS codon 12/13 (1/23, 4.3% vs. 11/21, 52%; p = 0.0005) and pathogenic TP53 mutation frequency (0/17, 0% vs. 7/21, 33.3%; p = 0.0108,) compared to prevalent cancers; 10/17 (58.8%) incident cancers harbored one or more truncating APC mutations, all showing mutational signatures of mismatch repair (MMR) deficiency. The proportion of MMR deficiency-related mutational events was significantly higher in incident compared to prevalent CRC (p = 0.018). In conclusion, our study identifies a set of features indicative of biological differences between incident and prevalent cancers in LS, which should further be monitored in prospective LS screening studies to guide towards optimized prevention protocols. [ABSTRACT FROM AUTHOR]

Some 10–50% of Lynch-suspected cases with abnormal immunohistochemical (IHC) staining remain without any identifiable germline mutation of DNA mismatch repair (MMR) genes. MMR proteins form heterodimeric complexes, giving rise to distinct IHC patterns when mutant. Potential reasons for not finding a germline mutation include involvement of an MMR gene not predicted by the IHC pattern, epigenetic mechanism of predisposition, primary mutation in another DNA repair or replication-associated gene, and double somatic MMR gene mutations. We addressed these possibilities by germline and tumor studies in 60 Lynch-suspected cases ascertained through diagnostics (n = 55) or research (n = 5). All cases had abnormal MMR protein staining in tumors but no point mutation or large rearrangement of the suspected MMR genes in the germline. In diagnostic practice, MSH2/MSH6 (MutS Homolog 2/MutS Homolog 6) deficiency prompts MSH2 mutation screening; in our study, 3/11 index individuals (27%) with this IHC pattern revealed pathogenic germline mutations in MSH6. Individuals with isolated absence of MSH6 are routinely screened for MSH6 mutations alone; we found a predisposing mutation in MSH2 in 1/7 such cases (14%). Somatic deletion of the MSH2-MSH6 region, joint loss of MSH6 and MSH3 (MutS Homolog 3) proteins, and hindered MSH2/MSH6 dimerization offered explanations to misleading IHC patterns. Constitutional epimutation hypothesis was pursued in the MSH2 and/or MSH6-deficient cases plus 38 cases with MLH1 (MutL Homolog 1)-deficient tumors; a primary MLH1 epimutation was identified in one case with an MLH1-deficient tumor. We conclude that both MSH2 and MSH6 should be screened in MSH2/6- and MSH6-deficient cases. In MLH1-deficient cases, constitutional epimutations of MLH1 warrant consideration. [ABSTRACT FROM AUTHOR]