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Background: RAS/BRAF mutations, mismatch DNA repair complex deficiency (MMRd)/microsatellite instability (MSI), and CpG methylator phenotype (CIMP) are key molecular actors in colorectal carcinogenesis. To date, conflicting evidence about the correlations between these molecular features has been reported., Materials and Methods: A retrospectively selected cohort of 123 CRCs was divided into 3 groups based on the molecular characteristics: MMR proficient (MMRp)/BRAF p.V600E mutated (BRAF mut ), MMRd/BRAF mut , and MMRd/BRAF wild type (BRAF wt ). MLH1 promoter (pMLH1) methylation status was assessed by pyrosequencing. For 82 samples the CIMP phenotype was evaluated using the EpiTect® MethyLight kit., Results: The MMRd/BRAF mut group showed a higher pMLH1 methylation rate compared to both the MMRd/BRAF wt and the MMRp/BRAF mut groups. Overall, the two MMRd groups had a higher methylation rate compared to the MMRp cases independently from the mutational status of BRAF (p-value <0.0001). The MMRd/BRAF mut group was characterized by a 90.0 % of CIMP high (CIMP-H) tumors of which 97.2 % were pMLH1 methylated. Instead, the MMRd/BRAF wt group presented 50.0 % of CIMP-H adenocarcinomas., Conclusions: Our study demonstrates that pMLH1 hypermethylation, MMRd, BRAF mut and CIMP phenotype do not completely overlap in CRC. These findings further refine the knowledge on the molecular landscape of CRC and may have critical implications also for the clinical management of the disease., Competing Interests: Declaration of Competing Interest The authors declare no conflict of interest regarding the publishing paper., (Copyright © 2024 Elsevier GmbH. All rights reserved.)

Background: Approximately 15 % of colorectal adenocarcinomas (CRCs) are characterized by an altered expression of DNA mismatch repair (MMR) proteins (i.e. MMR deficiency [MMRd]). Lymph node ratio (LNR) represents one of the most important prognostic markers in non-advanced CRCs. No significant data are available regarding LNR distribution depending on MMR status., Purpose of the Study: The aim of the present work was to compare pathological and clinical characteristics of MMRd tumors versus MMR proficient (MMRp) cases. Particular attention was paid to how these molecular sub-groups relate to the LNR., Materials and Methods: A mono-Institutional series of 1037 consecutive surgically treated stage I-IV CRCs were retrospectively selected and data were obtained from pathological reports. Cases were characterized for MMR/MSI status by means of immunohistochemistry or for microsatellite instability (MSI) analysis., Results: MMRd/MSI tumors (n = 194; 18.7 %) showed significant differences in comparison to MMRp lesions for sex (female prevalence 50.5 % vs 40.7 %; p = 0.013), age (74.2 vs 69.2; p < 0.001), location (right side; p < 0.001), diameter (larger than MMRp; p < 0.001), growth pattern (expansive pattern of growth; p < 0.001), peri- (p = 0.0002) and intra-neoplastic (p = 0.0018) inflammatory infiltrate, presence of perineural invasion (p < 0.001), stage (lower stage at presentation; p < 0.001), grade (higher prevalence of high-grade tumors; p < 0.001), and LNR (lower; p < 0.001)., Conclusions: MMRd/MSI tumors are a distinct molecular CRC subtype characterized by a significantly lower LNR in comparison to MMRp lesions. These data further support the prognostic impact of MMRd/MSI status in early-stage CRCs., Competing Interests: Declaration of Competing Interest None related to the current work., (Copyright © 2023 Elsevier GmbH. All rights reserved.)

In sessile serrated lesions (SSLs) with adenomatous dysplasia, the dysplastic component and the serrated component without dysplasia should be considered as part of the same lesion, classified as SSL with dysplasia. However, some of these lesions may actually represent collisions between a serrated polyp and a conventional adenoma. Further supporting the "collision theory", conventional adenomatous dysplasia may be found in association with hyperplastic polyps (HPs). In order to determine the molecular and biological landscape of conventional type dysplasia in serrated lesions, we collected 17 cases of colorectal serrated lesions with adenomatous dysplasia, classifying them as SSL with dysplasia (n = 10) or as mixed lesions comprising a HP component and a conventional adenomatous component (n = 7). We characterized the dysplastic and the non-dysplastic component of each lesion, after microdissection, through the targeted mutational analysis of 11 commonly altered genes in colorectal cancer (AKT1, APC, BRAF, CTNNB1, KIT, KRAS, NRAS, PDGFRA, PIK3CA, PTEN and TP53). We also characterized MMR and p53 status by immunohistochemistry. Overall, 14/17 (82.4 %) cases harbored a mutation in at least one of the two components. The most altered genes were BRAF in 10/17 (58.8 %) cases, APC in 2/17 (11.8 %) and TP53 in 4/17 (23.5 %). Among the SSL with dysplasia, the mutational profile was concordant between the two components in 7/10 (70 %) cases, while among the mixed lesions, the mutational profile was concordant in 1/7 (14.3 %). In all but two cases of SSL with dysplasia, MMR status was concordant between the two components of the serrated lesions. Our findings suggest that adenomatous dysplasia may develop in SSL as part of the serrated lesion, even if some SSL with dysplasia may actually be collision lesions. On the other hand, the polyps that are morphologically classifiable as mixed lesions composed of a HP and a conventional adenomatous component are more likely to be collision lesions., (Copyright © 2022 Elsevier GmbH. All rights reserved.)