Fátima Carneiro

Background: Mismatch repair-deficient (MMRd) colorectal cancers (CRCs) are highly mutated and immunogenic yet frequently escape immune elimination. Objective: To define how host immunity shapes the genomic architecture and tumour microenvironment of MMRd CRC. Design: We used a genetically engineered mouse model of MMRd CRC to compare tumour development in immunocompetent and immunodeficient hosts. Tumours were characterised for microenvironment composition, immunoregulatory pathways, mutational burden and genetic diversity. Immunogenicity of selected mutations was tested and findings were validated in human samples. Results: In immunocompetent hosts, immune pressure reduces tumour incidence through selective elimination of early neoplastic clones bearing immunogenic mutations, consistent with antigen-specific immunoediting. Tumours exhibit a suppressive microenvironment with reduced cytotoxic lymphocytes and elevated immune checkpoint proteins. Tumours from immunodeficient mice showed higher mutational burden, greater genetic diversity and enrichment of mutations absent in immunocompetent animals, several of which encode neoantigens that elicit CD8 ⁺ T cell responses. Analyses of human CRCs with high microsatellite instability (MSI-H) confirmed retention of the same immunogenic mutations, elevated mutational burden, reduced effector immune infiltration and expression of immune checkpoint proteins. These results support a dual mechanism of immune escape, immunoediting and local immunosuppression, allowing MMRd CRC tumours to persist despite immune recognition. Conclusion: We show that immunosurveillance plays a dual role in constraining tumour development and sculpting the genetic and immunological landscapes of MMRd tumours. This evasion strategy explains the paradox of immune-rich yet progressive MMRd tumours and highlights vulnerabilities that could be exploited by neoantigen-based or immune reactivation therapies.

The 6th Edition of the WHO Classification of Digestive System Tumours represents a significant update to the 5th edition. It integrates pathological, new molecular, and clinical insights to refine the taxonomy of digestive system neoplasms. The revised classification continues to emphasise standardisation in terminology, coding, and diagnostic criteria to facilitate global consistency in diagnosis, treatment, epidemiological reporting and research. Structural reorganisation of book chapters describes epithelial tumours by anatomical site, while separating neuroendocrine, mesenchymal and haematolymphoid tumours into dedicated chapters that are aligned with other WHO tumour volumes. Genetic tumour syndromes are classified by mechanisms, pathways and genes, whereas metastatic disease is comprehensively covered under other tumours and metastases. Key structural and diagnostic refinements include consolidation of gastric dysplasia entities; separation of duodenal/ampullary from jejuno‐ileal tumours; clearer categorisation of colorectal serrated polyps and novel carcinoma grading; introduction of small‐ and large‐duct intrahepatic cholangiocarcinoma as separate entities, and redefinition of undifferentiated carcinoma to include ‘carcinoma with mesenchymal differentiation’. Several new entities are introduced, including oesophageal epidermoid metaplasia, colorectal intramucosal adenocarcinoma, low‐grade tubuloglandular adenocarcinoma and lymphoglandular complex‐like adenocarcinoma, intraductal tubulopapillary and intraductal oncocytic papillary neoplasms of the bile ducts and sonic hedgehog hepatocellular adenoma. The concept of amphicrine‐like carcinoma (ALC) is distinguished from MiNEN and broadens the understanding of tumours with dual neuroendocrine–non‐neuroendocrine differentiation. Grading systems are simplified to two‐tier classifications (low/high grade) across precursor lesions, with enhanced criteria for neuroendocrine tumour grading. Anal canal neoplasia terminology is harmonised with human papillomavirus (HPV) related Lower Anogenital Squamous Terminology (LAST) and mass‐forming biliary and gallbladder cancer precursors share similar terminology. Finally, carcinoma of unknown primary (CUP) is included in a separate section for the first time, classified by molecular and immunophenotypic profiles to guide therapy. Overall, the 6th edition strengthens tumour diagnostic precision and molecular alignment across the digestive system.

Aims: There is a lack of published literature on the diagnostic reproducibility of oesophageal squamous dysplasia using a two‐tiered grading system.Methods and results: We identified 75 oesophageal biopsies, which were reviewed by 10 international pathologists twice (1500 total observations) with a > 4‐week washout period. Between rounds, a consensus meeting refining diagnostic criteria was held and an atlas was created to provide illustrations. Overall agreement was fair with kappa of 0.35 and 0.32 in round 1 and 2, respectively. Agreement was moderate to fair for negative for dysplasia (ND) (round 1 = 0.41 and round 2 = 0.34) and poor for indefinite for dysplasia (IND) and low‐grade dysplasia (LGD) (kappa N = 27) or HGD (N = 18). MDx was rarely achieved for LGD (N = 6). In round 2, MDx was seen in 49 (65%) cases (20 ND, 1 IND, 11 LGD and 17 HGD). Of the 40 cases with MDx for both rounds, 39 were concordant (15 HGD, 6 LGD and 18 ND).Conclusions: Overall agreement among pathologists in diagnosing squamous lesions is fair; however, HGD had good agreement. This study fills an important gap in our knowledge of the inter‐rater variability in the diagnosis of oesophageal squamous dysplasia.

Although it has been shown that the tumor extracellular matrix (ECM) may sustain the cancer stem cell (CSC) niche, its role in the modulation of CSC properties remains poorly characterized. To elucidate this, paired tumor and adjacent normal mucosa, derived from colon cancer patients’ surgical resections, were decellularized and recellularized with two distinct colon cancer cells, HT-29 or HCT-15. Methods: The matrix impact on cancer stem cell marker expression was evaluated by flow cytometry and qRT-PCR, while transforming growth factor-β (TGF-β) secretion and matrix metalloprotease (MMP) activity were quantified by ELISA and zymography. Results: In contrast to their paired normal counterparts, the tumor decellularized matrices enhanced HT-29 expression of the pluripotency and stemness genes NANOG (p = 0.0117), SOX2 (p = 0.0156), and OCT4 (p = 0.0312) and of the epithelial-to-mesenchymal transition (EMT)-associated transcription factor SNAI1 (p = 0.0156). Notably, no significant differences were found in the expression of SLUG or TGFB on HT-29 or of the six transcripts on HCT-15 cells. HT-29 mRNA alterations were followed by enhanced expression of the stemness-associated receptors cluster of differentiation 44 (CD44), CD133, and CD166 (p = 0.0078), the secretion of TGF-β (p = 0.0286), and MMP-2 (p = 0.0081) and MMP-9 (p = 0.0402) proteolysis. To infer the clinical relevance of these findings, we assessed cohort databases and evidenced that patients expressing higher levels of the four stemness-associated genes (NANOG/SOX2/OCT4/SNAI1) had worse overall survival. This study demonstrates that normal and tumor matrices harbor different stemness potential and suggest patient-derived decellularized matrices as an excellent three-dimensional (3D) model to unveil stemness signatures, appointing candidates for future therapeutic strategies.

Background: Gastric cancer (GC) patients from European (EU) and especially Latin American (LATAM) countries are underrepresented in previous large-scale multi-omic studies that have identified clinically relevant subgroups. The LEGACY study aimed to profile the molecular and immunological features of GCs from EU and LATAM countries. Methods: Tumor biopsies from 95 EU and 56 LATAM GCs were profiled with immunohistochemistry (CD3, CD8, FOXP3, PD-L1, MSI and HER2), Nanostring mRNA expression analyses, and microbiome sequencing. Results: Immune profiling identified four distinct immune clusters: a T cell dominant cluster with enriched activation pathways, a macrophage dominant cluster and an immune excluded microenvironment which were equally distributed among the countries. A fourth cluster of mostly Mexican patients consisted of excessive T cell numbers accompanied by enhanced cytokine signaling in absence of enhanced antigen presentation and cytotoxicity signatures and a strong association with H. pylori infection. Discussion: Both EU and LATAM countries have GCs with a T cell inflamed microenvironment that might benefit from checkpoint inhibition. We identified a highly inflamed GC subgroup that lacked antigen presentation and cytotoxicity associated with H. pylori CagA-positive strains, suggesting their contribution to tumor immune tolerance. Future studies are needed to unravel whether these cancers benefit from immunotherapy as well.

This case report describes a rare case of bi-phenotypic gastric cancer with two distinct, but clonally related, histological components. The first component, associated with Epstein-Barr virus (EBV) infection, exhibited the morphological features of gastric carcinoma with lymphoid stroma, suggesting that EBV, as an effective immunogenic factor, may trigger a prominent immune response within the tumour microenvironment. The second component, which was EBV-negative, displayed tubular/papillary morphology and features of increased biological aggressiveness, such as high-grade areas and lymphatic invasion. Immunohistochemical and molecular studies confirmed that, despite the differing morphologies and immunophenotypes, both components were clonally related, with the EBV-negative area showing more complex DNA aberrations, reminiscent of chromosomally instable (CIN) lesions. This case describes clonally related EBV-positive and -negative components within a single gastric cancer, contributing to a better understanding of EBV role in tumour heterogeneity and progression and highlights the impact of EBV loss on tumour behaviour.

Gastric and gastroesophageal junction adenocarcinomas (GA/GEJA) are associated with a poor prognosis, primarily due to late disease diagnosis. Human Epidermal Growth Factor Receptor 2 (HER2) overexpression and programmed death-ligand 1 (PD-L1) expression are important biomarkers for treatment selection in locally advanced unresectable and metastatic GA/GEJA, and there is increasing interest in their role in earlier stages of disease. In this study, we aimed to evaluate HER2 and PD-L1 expression in a curative-intent GA/GEJA cohort to describe their expression patterns and analyze the association between HER2 expression and clinicopathological features. HER2 expression was evaluated in surgical and endoscopic submucosal dissection tumor samples, and PD-L1 was evaluated in HER2-positive cases. The clinical cohort included 107 patients, with 8.4% testing positive for HER2 (seven of whom also exhibited a PD-L1 combined positive score of ≥1. HER2 status was not significantly associated with survival outcomes. A pathologist-guided, region-specific analysis revealed that PD-L1 expression rarely overlaps with HER2-positive tumor areas. While the therapeutic implications of these observations remain unknown, these findings suggest that combination strategies targeting HER2 and PD-L1 might be directed toward distinct tumor subclones. The herein disclosed region-specific biomarker expression patterns may have important therapeutic and prognostic impacts, warranting further evaluation.

Background: Conflicting results about the prognostic relevance of signet ring cell histology in gastric cancer have been reported. We aimed to perform a meta-analysis focusing on the clinicopathological features and prognosis of this subgroup of cancer compared with other histologies. Methods: A systematic literature search in the PubMed database was conducted, including all publications up to 1 October 2021. A meta-analysis comparing the results of the studies was performed. Results: A total of 2062 studies referring to gastric cancer with signet ring cell histology were identified, of which 262 studies reported on its relationship with clinical information. Of these, 74 were suitable to be included in the meta-analysis. A slightly lower risk of developing nodal metastases in signet ring cell tumours compared to other histotypes was found (especially to undifferentiated/poorly differentiated/mucinous and mixed histotypes); the lower risk was more evident in early and slightly increased in advanced gastric cancer. Survival tended to be better in early stage signet ring cell cancer compared to other histotypes; no differences were shown in advanced stages, and survival was poorer in metastatic patients. In the subgroup analysis, survival in signet ring cell cancer was slightly worse compared to non-signet ring cell cancer and differentiated/well-to-moderately differentiated adenocarcinoma. Conclusions: Most of the conflicting results in signet ring cell gastric cancer literature could be derived from the lack of standardisation in their classification and the comparison with the different subtypes of gastric cancer. There is a critical need to strive for a standardised classification system for gastric cancer, fostering clarity and coherence in the forthcoming research and clinical applications.