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Claudin-18.2 (CLDN18.2) is a member of the tight junction protein family and is a highly selective biomarker with frequent abnormal expression during the occurrence and development of various primary malignant tumors, including gastric cancer (GC) and esophago-gastric junction adenocarcinomas (EGJA). For these reasons, CLDN18.2 has been investigated as a therapeutic target for GC/EGJA malignancies. Recently, zolbetuximab has been proposed as a new standard of care for patients with CLDN18.2-positive, HER2-negative, locally advanced and metastatic GC/EGJA. The use of CLDN18 IHC assays to select patients who might benefit from anti-CLDN18.2 therapy is currently entering clinical practice. In this setting, pathologists play a central role in therapeutic decision-making. Accurate biomarker assessment is essential to ensure the best therapeutic option for patients. In the present review, we provide a comprehensive overview of available evidence on CLDN18.2 testing and its impact on the therapeutic management of patients with GC/EGJA, as well as some practical suggestions for CLDN18.2 staining interpretation and potential pitfalls in the real-world setting., Competing Interests: Declaration of Competing Interest FP received honoraria from BMS, MSD, Merck-Serono, Amgen, Takeda, Bayer, Servier, Astellas, Pierre-Fabre; research grants from Agenus, Amgen, Astrazeneca, Incyte, BMS. SL had roles as consultant or advisor for Amgen, Astra Zeneca, Bristol-Myers Squibb, Daiichi-Sankyo, Incyte, Lilly, Merck Serono, MSD, Servier, she received research funding from Amgen, Astellas, Astra-Zeneca, Bayer, BMS Daichii Sankyo, Hutchinson, Incyte, Merck Serono, Mirati, MSD, Pfizer, Roche and she is part of speakers’ bureau of Amgen, Bristol-Myers Squibb, GlaxoSmithKline, Lilly, Merck Serono, Pierre Fabre, Roche, Servier. MF had roles as consultant or advisor for Amgen, Astra Zeneca, Bristol-Myers Squibb, Incyte, Lilly, MSD, Astellas, GlaxoSmithKline, Roche, Pierre Fabre, he received research funding from Astellas, QED, Macrophage pharma, Diaceutics. FG has advisory board roles for GlaxoSmithKline and MSD, speakers honoraria from MSD, GlaxoSmithKline, Pierre Fabbre, Incyte., (Copyright © 2024 The Authors. Published by 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.)

Colorectal adenosquamous carcinoma (ASC) is exceedingly rare, comprising less than 0.1% of all colorectal malignancies, and is characterized by the admixture of glandular and squamous components. Due to its rarity, immunohistochemical and biological profiles have not been well investigated. The clinico-pathologic features of 29 cases of primary colorectal adenosquamous carcinomas, including four synchronous metastases, as well as the immunohistochemical expression of keratin 20, CDX2, keratin 34βE12, keratin 5/6, p63, p40, β-Catenin, Cyclin D1 and mismatch repair protein (MMR) expression in both squamous and glandular components are described. All ASCs showed aggressive clinico-pathologic features; all cases showed at least one aggressive pathologic characteristic (poorly differentiated, vascular invasion, infiltrative growth pattern) and 69% of cases were either stage III or IV. The squamous component was keratin 34βE12 positive in all cases and keratin 5/6 positive in 27 cases, while only 7 cases showed p63 and/or p40 expression. β-Catenin and Cyclin D1 showed different expression, with nuclear staining of Cyclin D1 in the squamous component of all cases (both primary and metastatic lesions) and nuclear staining of β-Catenin predominantly in the glandular component. All but one case showed proficient MMR profile. Sixteen patients (64%) died of their disease with median survival of 10 months. ASC show aggressive clinical outcome and aggressive pathologic characteristics. A peculiar keratin 34βE12 positive profile in the squamous component is seen differing from squamous cell carcinoma and non-intestinal ASC. The staining patterns for β-Catenin and Cyclin D1 between components, supports a possible divergent clonal evolution of the neoplasm., (Copyright © 2022 Elsevier GmbH. All rights reserved.)

The metastatic spread of breast carcinoma to the stomach is a rare event and often represents a diagnostic challenge. In the present study, 23 cases of gastric metastases from breast cancer were retrospectively identified dating back until 2007. Primitive histotype, localization, gross appearance, microscopic architecture were analyzed. Cytokeratins 7 and 20, sex hormones, HER2 and Ki67 expression was evaluated. According to the results, the series was characterized by an enrichment of lobular primitive histotype (43.7%). In most cases gastric metastases were described as parietal nodules, polypoid masses or ulcerated lesions, mainly involving the antro-angular region. In a relatively high rate (10.5%) of cases, endoscopic examinations resulted negative for macroscopic lesions. More than half of the cases (52.2%) microscopically resembled primitive poorly cohesive gastric cancer. Because gross and histological findings can be deceiving, immunohistochemistry may be essential for the diagnosis of gastric metastases from breast cancer. Accordingly with the results of our analysis and literature review, an immunohistochemical panel composed of cytokeratins 7 and 20, Estrogen and Progesteron Receptors would drastically improve diagnostic accuracy. Interaction among the clinician, endoscopist and the pathologist is also essential to provide the patient the best therapeutic option., (Copyright © 2022 Elsevier GmbH. All rights reserved.)