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AimsMucinous cystic neoplasms (MCN) are defined by the presence of an ovarian‐type stroma (OTS). Once ovarian stroma has become a requirement for the diagnosis of MCNs, studies using this criterion have disclosed that MCNs are seen almost exclusively (97%) in women. The occurrence of MCNs (with ovarian stroma) in men is exceedingly rare and raises questions about the origin of OTS and the role of hormones in tumourigenesis. This study aims to investigate the clinical and histopathological features of pancreatic or hepatic MCNs in men.Methods and resultsWe examined the MCN cases in men and compared them with age‐matched women. We further investigated MCN in premenopausal and postmenopausal women to explore the impact of hormonal status.The stromal cellularity tended to be lower in men as compared to women; however, limited numbers prevented statistical significance. Clinical presentation, tumour location, body mass index and cyst complexity were similar between men and age‐matched women, similarly in pre‐ and postmenopausal woman groups. All MCN cases, regardless of gender or hormonal status, showed OTS with positivity for oestrogen receptor (ER), androgen receptor (AR) and SF‐1 immunostains. Additionally, the presence of AR and ER‐beta in lining epithelial cells, in addition to the stromal cells, raised the probability for a potential role for local hormonal signalling in the pathogenesis of these tumours.ConclusionsMCNs in men had overlapping histopathologic and immunohistochemical profiles with those in women, regardless of menopausal status.

AimsThere is a lack of published literature on the diagnostic reproducibility of oesophageal squamous dysplasia using a two‐tiered grading system.Methods and resultsWe 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 <0.2). Agreement for high‐grade dysplasia (HGD) was good in both rounds (round 1 = 0.64; round 2 = 0.61). In round 1, majority diagnosis (MDx, ≥6 of 10 raters agreeing) was seen in 51 (68%) cases with the majority classified as ND (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).ConclusionsOverall 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.

Introduction. Increased steatosis on preimplant liver frozen section is associated with delayed graft function and primary nonfunction. Efforts to standardize histologic assessment have proven difficult. Frozen section artifact and lipopeliosis complicate the detection of steatosis. We aimed to develop and validate an AI model to recognize large droplet fat and fat induced artifact (FIA)/lipopeliosis on preimplantation frozen section and to correlate the AI results with post-transplant clinical parameters. Methods. The model was applied to 161 consecutive liver transplant specimens with preimplant slides. Results were correlated with traditional and Banff histologic assessment and clinical parameters. Results. By traditional assessment, steatosis ranged from 0%–40%. The AI model identified a range of 0 to 15.9% steatosis. There was no difference in patient survival by any measures of steatosis. AI steatosis correlated with increased risk of early allograft dysfunction (OR = 1.63, P < .001), respiratory failure (OR = 1.21, P = .003), and more advanced fibrosis (OR = 1.18, P = .030), but was not correlated with graft or patient survival. FIA/lipopeliosis were identified in a range of 0 to 6.42%. In univariate analysis the percentage of FIA/lipopeliosis correlated with both graft and patient survival ( P = .044 and P = .009, respectively), but was not associated with increased risk of early allograft dysfunction, respiratory failure, or advanced fibrosis. Conclusions. We developed an AI model that quantitates large droplet fat and FIA/lipopeliosis on frozen section slides and found a correlation with post-transplant outcomes. Further studies on larger, multi-institutional cohorts with higher fat containing donors are necessary to determine the role this model may have in organ acceptance decisions.

Aims The current American Joint Committee on Cancer (AJCC) staging manual and the College of American Pathologists (CAP) colorectal carcinoma (CRC) protocol specify use of a four‐tiered grading system (i.e. grades 1–4; well‐differentiated–undifferentiated) for CRC, based on percentage of gland formation. The World Health Organization (WHO) 5th edition grades CRC into low‐grade (well‐ and moderately differentiated) and high‐grade (poorly and undifferentiated), based on the least differentiated component. We studied interobserver agreement and practice patterns among pathologists when grading CRC by these two grading systems. Methods and results Five gastrointestinal pathologists reviewed 100 scanned CRC slides and graded the tumour on each slide, per provided criteria in (a) WHO 5th edition book, (b) AJCC manual/CAP CRC protocol and (c) their clinical practice. A questionnaire for grading selected CRC subtypes was also provided. Statistical analysis was performed using Pearson's χ 2 test and Fleiss multi‐rater kappa analyses. Overall, agreement among the five reviewers when grading via WHO and AJCC criteria for low‐grade and high‐grade CRC was moderate ( κ = 0.568, P < 0.001) and good ( κ = 0.611, P < 0.001), respectively. All reviewers graded significantly more tumours as high‐grade when using WHO (median = 46) versus AJCC/CAP criteria (median = 20). Conclusions Interobserver agreement was higher using the AJCC grading criteria as a two‐tiered system. Significantly more tumours were called high‐grade using the WHO criteria. This raises concerns regarding upgrading tumours, as well as potential differences in grading tumours among pathologists worldwide, based on regional preferred grading systems. Synchronisation of these two grading systems is necessary for uniform grading of CRCs throughout institutions.

251 Background: The development of colorectal liver metastases (CRLM) is associated with poor prognosis, and recent data suggest that metastasis to the liver is associated with resistance to immunotherapy. We characterized the microenvironment of primary colorectal carcinomas (CRCs) relative to their synchronous CRLM using a validated segmentation algorithm that quantifies 15 distinct morphologic tumor features. Methods: Adult CRC patients with synchronous CRLM (N=57) at Mayo Clinic were identified from the electronic health record using Epic Slicer Dicer and from an internal database. Tumor H&E sections were digitized and reviewed for quality control (RKP). QuantCRC (Aiforia, Inc) was applied to digitized images to extract 15 GI pathologist pre-defined morphological features. Tumor features were compared between primaries and CRLM using the Kruskal–Wallis test. The project was approved by the Mayo Clinic Institutional Review Board. Results: The study included 57 patients (median age 59 years [IQR 50, 73], 51% female) with CRC primaries and synchronous CRLM. Among primaries, 20 (35%) were right-sided and 37 (65%) were left-sided. QuantCRC identified 6 of 15 morphological features that differed significantly between primaries and their CRLM, including reduced stroma, more high-grade and necrosis, and a higher tumor: stromal ratio (TSR) in CRLM (Table). The increase in TIL density in CRLM vs the primary tumor was of borderline significance (p =0.053). Among patients with left-sided primary tumors, their CRLM had significantly higher TSR, percent high-grade, percent necrosis, and TIL density compared to the primary (all p values ≤ 0.02). Among right sided primaries, CRLM had a significantly reduced percent mature stroma (p=0.034) whereas percent necrosis was increased (p =0.01). Conclusions: Using deep learning, we identified tumor morphological features that differed significantly between primary CRC and their synchronous CRLM. This included higher TSR in CRLMs compared to primaries that is associated with epithelial-mesenchymal transition and has been shown to contribute to treatment resistance. Analysis of tumor morphological features with patient prognosis is ongoing. Deep learning-derived morphological features of primary CRC and CRLM. Morphological feature (Median) Primary tumor Liver metastasis P-value Tumor-Stroma Ratio 0.78 1.50 0.008 % High-grade 23.08 31.72 0.005 TIL Count 44.36 60.20 0.053 % Necrosis 6.35 19.32 <0.001 %Signet Ring Cells 0.25 0.13 0.088 TB/PDC 0.89 1.13 0.484 % Stroma 54.89 40.98 <0.001 % Immature Stroma 46.76 34.13 <0.001 % Mature Stroma 6.27 5.08 0.030

732 Background: Ampullary carcinoma (AC) is a rare malignancy arising from the ampulla of Vater which has a more favorable prognosis compared to other pancreatic malignancies. Current guidelines favor surgical resection followed by adjuvant therapy for average risk patients (pts), however the type of regimen as well as other perioperative treatment modalities are still being explored. The objective of this retrospective study aims to provide insight into the management of locoregional disease. Methods: Pathology records from Mayo Clinic (AZ, FL, MN) denoting AC between 2010 to 2024 were searched using Mayo Data Explorer and selected for retrospective review. Pt demographics, treatment courses, and next generation sequencing (NGS) data were collected. Statistical analysis was conducted using SAS version 9.04. Results: A total of 137 pts (62% male, n = 85) were identified with median age 66 years old. Histologic subtypes were 54% pancreatobiliary (44/81), 40% intestinal (32/81), 6% mixed (5/81), with 56 pts unknown. Stages at diagnosis were 81% resectable (111/137), 11% locally advanced (15/137), and 8% metastatic (11/137). Nearly all (93%, n = 103/111) pts with localized disease had resection with a 97% R0 resection rate (100/103). Majority (68%, n = 75/111) of resectable pts had perioperative chemotherapy with 5-FU or gemcitabine-based regimens (24%, n = 18/75 neoadjuvant vs. 76%, n = 57/75 adjuvant). Perioperative chemoradiation was given in 17% (19/111) of pts. At median follow up of 30.5 months, recurrence rates were 40% (41/103), primarily to the liver (18/41). Median recurrence free survival (RFS) was 29.3 months (95% CI 24.7 – NE). Median overall survival (OS) has not been reached. The 5-year RFS and OS rates were 0.37 (95% CI 0.25 - 0.55) and 0.69 (95% CI 0.58 - 0.82), respectively. Univariate analysis showed no difference in OS with the addition of neoadjuvant or adjuvant chemotherapy or chemoradiation. Somatic NGS testing showed pathogenic mutations in 90% of pts (63/70): 57% KRAS (36/63; 44% G12D, 19% G12V, 8% G12C, 8% G12D, 19% others); 13% homologous recombination (HR) (8/63); 6% ERRB2 /Her2 amplification (4/63), and 5% mismatch repair (MMR) (3/63). Conclusions: AC has a favorable prognosis in resectable pts. However, high recurrence rates indicate the need for better systemic therapies and improved selection of pts who would benefit from these treatments. Future research should focus on refining perioperative strategies to enhance outcomes and reduce recurrence.

Abstract Background Histologic inflammation persists in up to 1/4 of patients with Crohn’s disease (CD) despite endoscopic mucosal healing. Histologic and combined endoscopic-histologic endpoints are evolving measures of treatment efficacy in CD; however, the impact of histologic healing on long-term outcomes and disease progression is unknown. Week (W) 52 data comparing mirikizumab (Miri) vs placebo (PBO) in the randomized, double-blind, placebo- and active-controlled, treat-through Phase 3 VIVID-1 trial in patients with moderately-to-severely active CD (NCT03926130) were reported previously.1 Methods The main objective was to evaluate the association of W12 histologic response and W12 histologic remission with W52 clinical and endoscopic outcomes in VIVID-1. Two biopsy specimens from each of 5 intestinal segments (1 ileal and 4 colonic) were obtained from the edge of the ulcers, or the most inflamed mucosa from randomized patients at screening, W12, and W52. All analyses were post hoc and among patients with active histologic disease (defined as a Robarts Histopathology Index &gt;0 and a Global Histologic Disease Activity Score &gt;0) at baseline. Results At W12, treatment with Miri resulted in statistically significantly higher rates of achieving histologic response and histologic remission vs. PBO (Figure). At W12, 62.1% of patients had agreement (k=0.27 [fair]) between histologic response and endoscopic response, with a greater percentage achieving histologic over endoscopic response (59.0% vs. 38.8%)*. Significantly greater proportions of patients who achieved histologic response at W12 also achieved histologic response, histologic remission, endoscopic response, endoscopic remission, combined CDAI (Crohn’s Disease Activity Index) remission and endoscopic response, and normalisation of faecal calprotectin levels ≤250 µg/g and ≤150 µg/g at W52 (Table). Similar associations were observed between W12 histologic remission and W52 outcomes. Conclusion Histologic response seems to be an early objective sign of anti-inflammatory response and was significantly associated with one-year endoscopic and histologic outcomes, as well as biomarker normalisation. *Observed data References 1.Jairath V, et al. Presented at: UEGW 2024. OP131.

PURPOSE Pancreatic acinar cell carcinoma (PACC) is a rare and aggressive form of pancreatic cancer that originates in the acinar cells of the exocrine pancreas. In this study, we aimed to investigate the clinical and molecular characteristics of patients with PACC at our institution. METHODS This was a retrospective study of patients with PACC seen at Mayo Clinic between 2002 and 2023. Baseline patient characteristics, tumor pathology, treatment strategies used, and survival outcomes were analyzed. Kaplan-Meier curves were estimated using newsurv macros in SAS. RESULTS The study included a total of 65 patients with PACC. The median age at diagnosis was 66 years. Almost half of the patients (48%) presented with resectable/borderline-resectable disease (n = 28). Five-year overall survival (OS) for resectable/borderline-resectable, locally advanced/unresectable, and metastatic disease were 72.0%, 21.6%, and 20.9%, respectively. Somatic and germline next-generation sequencing identified numerous potentially actionable targets including homologous recombination (43% somatic, 33% germline), RAF alterations (29% somatic), and mismatch repair (14% somatic). CONCLUSION Our findings underscore the heterogeneity and aggressive nature of PACC. Despite the improved prognosis for patients with resectable/borderline-resectable disease, OS remains poor, particularly for those with locally advanced or metastatic disease. The identification of actionable molecular targets in a significant proportion of patients highlights the potential for personalized therapeutic approaches. Future research should focus on tailored treatment strategies to exploit these molecular vulnerabilities, which may offer new options for improving outcomes in this rare malignancy.