Ceramide deficiency in the stratum corneum (SC) is a key etiological factor in atopic dermatitis (AD). To clarify the direct role of SC ceramide depletion in impairing SC barrier and water-holding functions and in initiating AD-like skin symptoms and disease-specific molecular alterations, we generated Tg mice overexpressing a mutant form of acid ceramidase (aCDase) under the control of the involucrin promoter, resulting in targeted expression in the upper epidermis. By 3 weeks of age, Tg mice developed noninflammatory, scaly skin characterized by severely compromised barrier integrity and water-holding capacity, along with significantly elevated epidermal aCDase activity and markedly reduced ceramide levels in the SC. Compared to WT controls, Tg mice also exhibited increased epidermal innervation and reduced intraepidermal semaphorin 3a protein levels. Additionally, Tg skin showed substantial changes in the expression of AD-associated biomarkers involved in barrier impairment, pruritus, and Th2 polarization. These included increased levels of Il10, Il17a, S100a7, S100a8, and S100a9 and decreased levels of Cxcl10, Ifng, Il2, Il13, Il33, Sema3a, and Tlr9. Repeated topical application of mite antigens induced allergic responses in Tg mice, but not in WT mice. These responses were characterized by prominent eosinophil infiltration in the dermis and significantly elevated serum IgE levels. Allergen-challenged ear skin from Tg mice also demonstrated significantly increased expression of inflammatory mediators related to AD, including Ccl17, Ccl22, Ccl26, Ccl27, Il3, Il13, Il22, and Il33. These findings establish Tg mice as a pathophysiologically relevant model of AD, presenting key features such as xerotic, pruritic skin, impaired barrier and water-retention functions, and Th2-dominant allergic inflammation. This model provides important insights into ceramide-dependent mechanisms in AD pathogenesis and offers a useful platform for therapeutic development. © 2026 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The extracellular matrix (ECM) plays a pivotal role in facilitating tumour development, invasiveness, metastasis, and immunoevasive processes through dynamic ECM remodelling processes. Testican-1 (SPOCK1), an excretory matricellular proteoglycan, is suggested to exert a role in the facilitation of ECM remodelling processes through interacting with matrix metalloproteases (MMPs) and even its less known forms. The structural mechanisms of interactions between testican-1 and MMPs were studied, and their roles in tumour-promotion pathway processes were also examined using a computational approach and immunofluorescence validated by colocalisation technique analysis. A computational analysis using docking, molecular dynamics (MD), and systems biology analysis was employed. HDock and GROMACS were chosen to analyse binding affinity and testican-1 stability with 28 different MMPs. H-bond, free energy, and root mean square fluctuation (RMSF) analyses were performed to confirm the interactions in the testican-1-MMP complexes. The systems biology toolkit implemented in this study consisted of STRING, BioGRID, and Cytoscape, which were employed for testican-1 interaction network and pathway analysis. Kaplan-Meier survival analysis using the GEPIA2 tool was utilised to correlate SPOCK1 gene expression and clinical survival measures for various malignancies. The docking analysis showed robust interactions between testican-1 and MMP23, MMP25, and MMP28. Additionally, testican-1-MMP complexes were confirmed to form stable interfaces based on comprehensive MD analysis, suggesting solid binding interfaces with the MMP-unique domain of testican-1. Our systems biology experiment indicated testican-1 as a central hub for interactions between immunoevasive and ECM remodelling processes. SPOCK expression was also shown to correlate with significant survival measures for different malignancies, revealing clinical implications in cancer. The testican-1-MMP computational analysis suggests testican-1 plays a pivotal role as a therapeutic target for a wide range of malignancies. SPOCK-MMP interactions could be targeted to interrupt tumour-promoting processes by arresting dynamic changes in the ECM, thereby improving patient survival. © 2026 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The fallopian tube epithelium (FTE) is the primary tissue of origin for ovarian high-grade serous carcinoma (HGSC), with ovulation implicated as a key risk factor. TP53 mutations, a hallmark of HGSC and its precursor lesions, such as p53 signature, are predominantly CG>TA substitutions attributed to cytidine deamination. We previously demonstrated that ovulatory follicular fluid (FF) released reactive oxygen species (ROS), which activate activation-induced cytidine deaminase (AID) and promote TP53 mutagenesis in FTE. Here, we demonstrate that hemoglobin (Hb) originating from retrograde menstruation acts as an extracellular ROS scavenger, attenuating AID-mediated TP53 deamination in fallopian tube fimbriae, both in vitro and in vivo. Peritoneal fluid from tubal-ligated women exhibited significantly lower Hb, higher ROS, and elevated hypoxanthine phosphoribosyl transferase (HPRT) mutagenic activity compared to nonligated controls (p < 0.004). Histopathological analysis of 206 fallopian tubes from 119 women undergoing opportunistic salpingectomy further revealed a significantly higher frequency of p53 signatures in ligated tubes (0.22 ± 0.64 lesions per fimbria) than in nonligated tubes (0.07 ± 0.31 lesions per fimbria) (p = 0.017). Multivariate analysis identified tubal ligation as the sole reproductive factor independently associated with p53 signatures [odds ratio (OR) = 3.32; 95% CI: 1.15-9.57]. Our findings indicate that retrograde menstrual Hb mitigates ovulation-associated ROS stress, thereby reducing AID-mediated TP53 mutagenesis in the FTE. This study uncovers a physiological, protective role for menstruation against ovulatory oxidative damage and its mutagenic consequences, while demonstrating that tubal ligation disrupts this endogenous antioxidant mechanism, resulting in an increased burden of p53 signature lesions. © 2026 The Pathological Society of Great Britain and Ireland.

Angioimmunoblastic T-cell lymphoma (AITL) exemplifies a neoplasm characterized by prominent inflammatory infiltration and robust immune responses in the tumor microenvironment (TME). The pathophysiology of refractory/recurrent (RR) AITL remains poorly understood due to profound intratumoral heterogeneity and complex TME features, contributing to limited therapeutic efficacy. Using Xenium-based spatial transcriptomics on 10 clinical samples, we compared RR AITL with treatment-responsive [non-refractory/recurrent event in 3 years (NR)] cases to map the TME architecture. We identified a novel cluster of NEIL3+ (Nei Like DNA Glycosylase 3) T-follicular helper (Tfh) cells, which exhibited stem-like characteristics at the transcriptional level, featuring self-renewal and multilineage differentiation capacity, and were highly enriched in RR tumors. Furthermore, we found major differences in immune cell organization between NR and RR microenvironments: RR cases were dominated by B cells primed for adaptive immunity and myeloid cells driving angiogenesis, whereas NR cases exhibited a chemokine-mediated regulatory landscape. These findings provide comprehensive characterization of the TME ecosystem in AITL and reveal potential therapeutic targets for high-risk RR AITL patients. © 2026 The Pathological Society of Great Britain and Ireland.

Efferocytosis is a process that maintains tissue homeostasis by removing apoptotic cells (ACs) by professional or non-professional phagocytes. The intricate process can be categorized into recognition of ACs, engulfment of ACs, and degradation of efferosomes. Aberrations in efferocytosis result in inadequate clearance of ACs, leading to prolonged inflammation that is implicated in the development and progression of various human diseases. Most central nervous system (CNS) diseases are associated with dysregulation of inflammatory homeostasis. Microglia, the resident immune cells of the CNS, play a primary role in efferocytosis in the brain, which is essential for maintaining the homeostasis of the internal environment. In this review, we summarize the current knowledge of the basic processes of efferocytosis and its indispensable role in the developing and aging brain. Additionally, we discuss the regulatory role of immune-metabolism crosstalk and the insights from single-cell sequencing analysis in dissecting microglial heterogeneity during efferocytosis. We also focus on recent discoveries regarding the critical role of efferocytosis in several CNS diseases, including cerebral ischemia, intracerebral hemorrhage, traumatic brain injury, major depressive disorder, glioblastoma multiforme, Alzheimer's disease, and Parkinson's disease. Finally, we outline potential therapeutic strategies and existing challenges, emphasizing the need for context-specific targeting to improve CNS disease outcomes. © 2026 The Pathological Society of Great Britain and Ireland.

Colorectal cancer (CRC) typically originates from benign polyps within the colorectum. However, the mechanisms driving this transformation remain poorly understood. In this study, we employed a comprehensive multi-omics approach, incorporating multiplex immunostaining and adeno-associated virus (AAV)-mediated mouse models, to systematically dissect the key drivers of malignant transformation in CRC. Our investigations revealed a dynamic and stage-specific expression pattern of thrombospondin 2 (encoded by the gene THBS2), characterized by significantly downregulated expression during the polyp stage, followed by markedly upregulated expression in malignant CRC tissues compared to healthy colon tissue. Intriguingly, THBS2 expression was primarily localized within a distinct fibroblast subpopulation, with THBS2+ fibroblasts exhibiting a tumor-tropic infiltration pattern. Through a series of analyses, we hypothesized that THBS2+ fibroblasts may play a role in coordinating CRC progression via the THBS2-CD36 and THBS2-SDC1 pathways. Furthermore, depletion of THBS2+ fibroblasts enhanced polyp formation but suppressed tumor formation in a thymidine kinase 1/ganciclovir/azoxymethane/dextran sulfate sodium mouse model. The comprehensive multi-omics atlas and complementary data presented here will advance our understanding of the mechanisms underlying CRC malignant transformation and may provide a potential therapeutic target. © 2026 The Pathological Society of Great Britain and Ireland.

Bile duct tumor thrombus (BDTT), a tumor cluster occupying the luminal space in the large bile duct, is rare in intrahepatic cholangiocarcinoma (iCCA). Most studies on BDTT in iCCA to date are case reports, and the clinicopathological characteristics remain unknown. This study aimed to characterize iCCA with BDTT clinicopathologically and genetically. We analyzed 223 surgically resected iCCA cases, including 102 small duct type (SDT) and 121 large duct type (LDT) cases. BDTT was found in 19.6% (20/102) of SDT cases. Histological and immunohistochemical features of BDTT-positive SDT were comparable with those of conventional SDT (MUC1+MUC2-MUC5AC-MUC6+/-CDX-2-). BDTT-positive SDT showed female predominance and higher T factors compared with conventional SDT. SDT was associated with a significantly longer survival in iCCA. SDT patients with BDTT had significantly shorter survival than those without BDTT and survival rates similar to those of LDT patients; the presence of BDTT in SDT was an independent unfavorable prognostic factor (HR = 2.601, p = 0.006). Whole-exome sequencing analysis revealed recurrent altered gene expression: those more frequent in SDT compared with LDT (BAP1, IDH1/2, ZNF717, FGFR2, NRAS); those more frequent in LDT (KRAS, TP53, SMAD4, MUC6, CACNA1A, MLL2, MDM2, TGFBR1/2); and those found comparably in both SDT and LDT (MUC4, ARID1A, EPHA2, PIK3CA, MUC17, MAP3K4, MUC2, BRAF, NF1). Genetic landscapes were similar in SDT iCCA with and without BDTT; recurrent mutations in MUC2 and MUC17 and FGFR2 fusion genes were more frequent in BDTT-positive SDTs. PTPRK::RSPO3 fusion gene was found in one LDT case. Intraglandular papillary and tubular proliferation is a unique and rare histology of SDT. BDTT was frequently found in SDT with this pattern, and FGFR2 gene rearrangement was frequent. These results highlight the importance of evaluating BDTT in SDT, as it may be the main route of hilar extension in aggressive cases. © 2026 The Pathological Society of Great Britain and Ireland.

Artificial intelligence (AI) and deep learning (DL) are transforming cancer research and clinical care, with histopathology playing a central role in this transformation. In colorectal cancer (CRC), the second leading cause of cancer mortality world‐wide, multimodal and vision‐language models (VLMs) hold particular promise for enhancing the standardisation of histopathology reporting, the understanding of disease biology, and the discovery of novel prognostic indicators. Despite the availability of guidelines and reporting templates for essential prognostic indicators, variability remains in how key features such as TNM staging or tumour deposits are assessed and reported in routine clinical practice. AI‐based tools have the potential to support refined extraction of established and extended features directly from whole‐slide images. In parallel, recent studies have shown that DL models applied to pathology slides and associated AI‐based biomarkers can outperform traditional histopathological prognostic indicators and uncover novel parameters, including tumour‐adipocyte interactions, tumour‐stroma ratio, and immune cell patterns at the invasive margin. Here, we review recent advances in both domains: AI‐assisted standardisation of CRC pathology reporting and AI‐driven identification of novel prognostic biomarkers. We highlight the need to refine and standardise CRC reporting practices and propose that a harmonised approach combining established pathology features with AI‐derived prognostic indicators could refine risk assessment and improve outcomes for CRC patients. © 2026 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.