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Aims Methods and results Conclusions Neuroendocrine tumours (NETs) occurring in the extrahepatic biliary system are exceedingly rare. While NETs typically manifest as mass lesions, the occurrence of microscopic neuroendocrine cell proliferation without a distinct mass remains undocumented at this location. This study aims to characterise the clinicopathological features of a series of well‐differentiated neuroendocrine lesions involving the extrahepatic biliary tree, including mass forming NETs and microscopic non‐mass‐forming neuroendocrine cell proliferation, designated neuroendocrine cell micronests (NCMs).Surgical resections of NETs/NCMs involving the extrahepatic bile ducts and gallbladder were identified from electronic pathology databases among seven institutions spanning from January 2011 to September 2023. Clinical and histological findings were recorded. Ten patients (four female, six male: age range = 34–75 years) were included in the study. Histopathological examination revealed visible mass‐forming lesions in four cases (1.6–14.0 cm in size), identified in the gallbladder (n = two) or extrahepatic bile duct (n = two), all diagnosed as well‐differentiated NETs. The remaining six cases revealed incidental non‐mass‐forming NCMs in either the cystic duct (n = two), common bile duct (n = three) or gallbladder (n = one), ranging from < 0.1 to 0.4 cm; four were associated with biliary lithiasis. No evidence of metastasis or recurrence was seen in the follow‐up period (range = 0.1–11.2 years).This study highlights the spectrum of extrahepatic biliary well‐differentiated neuroendocrine lesions, ranging from incidental microscopic NCMs to grossly apparent mass‐forming NETs, potentially requiring different clinical management. Noteworthy is the frequent association of incidental microscopic neuroendocrine cell proliferations with biliary lithiasis, indicating a potential neuroendocrine metaplastic pathogenesis that merits further exploration. [ABSTRACT FROM AUTHOR]

Neoadjuvant therapy (NAT) for early-stage pancreatic ductal adenocarcinoma (PDA) has recently gained prominence. We investigated the clinical significance of mucin 5 AC (MUC5AC), which exists in two major glycoforms, a less-glycosylated immature isoform (IM) and a heavily glycosylated mature isoform (MM), as a biomarker in resected PDA. Immunohistochemistry was performed on 100 resected PDAs to evaluate the expression of the IM and MM of MUC5AC using their respective monoclonal antibodies, CLH2 (NBP2-44455) and 45M1 (ab3649). MUC5AC localization (cytoplasmic, apical, and extra-cellular (EC)) was determined, and the H-scores were calculated. Univariate and multivariate (MVA) Cox regression models were used to estimate progression-free survival (PFS) and overall survival (OS). Of 100 resected PDA patients, 43 received NAT, and 57 were treatment-naïve with upfront surgery (UpS). In the study population (n = 100), IM expression (H-scores for objective response vs. no response vs. UpS = 104 vs. 152 vs. 163, p = 0.01) and MM-MUC5AC detection rates (56% vs. 63% vs. 82%, p = 0.02) were significantly different. In the NAT group, MM-MUC5AC-negative patients had significantly better PFS according to the MVA (Hazard Ratio: 0.2, 95% CI: 0.059–0.766, p = 0.01). Similar results were noted in a FOLFIRINOX sub-group (n = 36). We established an association of MUC5AC expression with treatment response and outcomes. [ABSTRACT FROM AUTHOR]

Invasive lobular breast cancer (ILC) is characterized by a relatively high risk for late recurrence and a unique metastatic pattern with an increased risk for metastasis to gynecologic organs and peritoneum. We present a unique case of recurrent ILC with metastasis to the abdominal peritoneum as well as the uterine myometrium and cervix. Treatment was complicated by the discovery of concomitant uterine carcinosarcoma. This patient was effectively treated with a combination of hormonal therapy for her metastatic ILC and a combination of chemotherapy and immunotherapy for uterine carcinosarcoma. Molecular evaluation revealed a characteristic CDH1 mutation within the ILC and a PI3KCA mutation within the uterine carcinosarcoma, both of which have been linked to epithelial-to-mesenchymal transitions. Examination of the tumor immune microenvironment revealed proportionally more cytotoxic NK cells. This robust immune infiltration may be an indicator of the response to immunotherapy observed in this tumor or a result of the metastatic breast cancer within the uterus. This report provides a characterization of the molecular and immunologic landscape in this case with metastatic ILC and uterine carcinosarcoma. [ABSTRACT FROM AUTHOR]

Quadruple-negative breast cancer (QNBC) is a triple-negative breast cancer (TNBC) subtype that lacks expression of the androgen (AR) receptor. Few studies have focused on this highly aggressive breast cancer, portending worse survival rates. We aimed to determine the following: (1) QNBC's molecular and clinical characteristics and compare them with other subtypes and (2) QNBC's association with clinicopathological factors and prognostic markers. We performed immunohistochemical evaluations of ARs on tissue tumor microarrays from FFPE tumor blocks of invasive ductal breast carcinomas in 202 African American women. Univariate analysis was performed using the chi-square test, with survival rates calculated using Kaplan–Meier curves. Overall, 75.8% of TNBCs were AR-negative. Compared to the luminal subtypes, TNBC and QNBC tumors were likely to be a higher grade (p < 0.001); HER2+/AR- and QNBCs were also larger than the other subtypes (p < 0.001). They also expressed increasing mean levels of proteins involved in invasion, such as CD44, fascin, and vimentin, as well as decreasing the expression of proteins involved in mammary differentiation, such as GATA3 and mammaglobin. We found no association between QNBC and stage, recurrence-free survival, or overall survival rates. The high prevalence of TNBC AR-negativity in these women could explain observed worse outcomes, supporting the existence of the unique QNBC subtype. [ABSTRACT FROM AUTHOR]

Aims: Ocrelizumab is a humanized anti‐CD20‐monoclonal antibody that has recently been approved for the treatment of certain types of multiple sclerosis. Isolated case reports of ocrelizumab‐associated colitis have been reported in the literature. We present a case series of ocrelizumab‐associated intestinal injury with a focus on histopathologic features and report a case of ocrelizumab‐associated hepatitis. Methods and results: A retrospective computerized search was conducted from 03/2017 to 08/2022, which identified six patients with suspected or clinically confirmed ocrelizumab‐associated intestinal injury and one patient with hepatic injury. Pertinent clinical, endoscopic, and histopathologic findings were reviewed and recorded. Seven patients (six female, one male) were identified with ages ranging from 24 to 68 years. The presenting symptoms included diarrhoea (n = 5), abdominal pain (n = 3), hematochezia (n = 2), and vomiting (n = 1), nausea (n = 1) fever (n = 1), and weight loss (n = 1). Endoscopic findings ranged from normal (n = 1) to patchy colonic inflammation with or without ulceration (n = 4) and decreased mucosal vascular pattern in the rectum (n = 1). Crohn's disease was clinically suspected in two patients and ulcerative colitis in one patient. None of the patients had a prior confirmed diagnosis of inflammatory bowel disease. Histologic patterns of initial colonic injury included acute colitis/proctitis (n = 5), and chronic active colitis (n = 1). Follow‐up ranged from 1 to 3 years and 10 months. All patients were alive at follow‐up. Follow‐up biopsies were available for four patients and findings included focal acute colitis (n = 1), apoptotic colopathy (n = 1) lymphocytic colitis (n = 1), and normal mucosa (n = 1). Four patients were treated with steroids and ocrelizumab was discontinued in three patients. Two patients were symptomatically managed with subsequent resolution of symptoms. The liver biopsy from the patient with a marked hepatic pattern of liver enzyme elevation showed an acute hepatitis pattern of injury with prominent centrilobular necrosis, which resolved upon discontinuation of the drug and treatment with steroids and azathioprine. Conclusions: The histologic manifestations of ocrelizumab‐associated intestinal injury are variable and can mimic inflammatory bowel disease. Hepatic injury can rarely manifest as an acute hepatitis pattern of injury with necrosis. Identifying ocrelizumab‐associated injury is paramount in determining management, which often includes discontinuation of ocrelizumab therapy, and/or administration of immunosuppressive therapy. [ABSTRACT FROM AUTHOR]

Background: Mismatch‐repair (MMR)/microsatellite instability (MSI) status has therapeutic implications in endometrial cancer (EC). The authors evaluated the concordance of testing and factors contributing to MMR expression heterogeneity. Methods: Six hundred sixty‐six ECs were characterized using immunohistochemistry (IHC), MSI testing, and mut‐L homolog 1 (MLH1) methylation. Select samples underwent whole‐transcriptome analysis and next‐generation sequencing. MMR expression of metastatic/recurrent sites was evaluated. Results: MSI testing identified 27.3% of cases as MSI‐high (n = 182), MMR IHC identified 25.1% cases as MMR‐deficient (n = 167), and 3.8% of cases (n = 25) demonstrated discordant results. A review of IHC staining explained discordant results in 18 cases, revealing subclonal loss of MLH1/Pms 1 homolog 2 (PMS2) (n = 10) and heterogeneous MMR IHC (mut‐S homolog 6 [MSH6], n = 7; MLH1/PMS2, n = 1). MSH6‐associated Lynch syndrome was diagnosed in three of six cases with heterogeneous expression. Subclonal or heterogeneous cases had a 38.9% recurrence rate (compared with 16.7% in complete MMR‐deficient cases and 9% in MMR‐proficient cases) and had abnormal MMR IHC results in all metastatic recurrent sites (n = 7). Tumors with subclonal MLH1/PMS2 demonstrated 74 differentially expressed genes (determined using digital spatial transcriptomics) when stratified by MLH1 expression, including many associated with epithelial–mesenchymal transition. Conclusions: Subclonal/heterogeneous MMR IHC cases showed epigenetic loss in 66.7%, germline mutations in 16.7%, and somatic mutations in 16.7%. MMR IHC reported as intact/deficient missed 21% of cases of Lynch syndrome. EC with subclonal/heterogeneous MMR expression demonstrated a high recurrence rate, and metastatic/recurrent sites were MMR‐deficient. Transcriptional analysis indicated an increased risk for migration/metastasis, suggesting that clonal MMR deficiency may be a driver for tumor aggressiveness. Reporting MMR IHC only as intact/deficient, without reporting subclonal and heterogeneous staining, misses opportunities for biomarker‐directed therapy. Plain Language Summary: Endometrial cancer is the most common gynecologic cancer, and 20%–40% of tumors have a defect in DNA proofreading known as mismatch‐repair (MMR) deficiency.These results can be used to guide therapy.Tests for this defect can yield differing results, revealing heterogeneous (mixed) proofreading capabilities.Tumors with discordant testing results and mixed MMR findings can have germline or somatic defects in MMR genes.Cells with deficient DNA proofreading in tumors with mixed MMR findings have DNA expression profiles linked to more aggressive characteristics and cancer spread.These MMR‐deficient cells may drive tumor behavior and the risk of spreading cancer. Intratumoral heterogeneity, including subclonal and heterogeneous mismatch‐repair (MMR) expression, can yield discordant results from diagnostic assays, such as immunohistochemistry and polymerase chain reaction‐based microsatellite instability testing. Within endometrial cancers, subclonal or heterogeneous MMR expression may be attributed to germline or somatic mutations in MMR proteins, and the authors demonstrate that these tumors are characterized by clonal selection favoring the propagation of MMR deficiency at sites of metastasis or recurrence. [ABSTRACT FROM AUTHOR]

Sarcomas in cytology fluids are uncommon, accounting for an estimated 3-6% of malignant effusions. High-grade endometrial stromal sarcomas are uncommon malignancies, whose true frequency is not well defined. We present a case of high-grade endometrial stromal sarcoma with a BCOR translocation metastatic to the pleural fluid. A 31-year-old female with a long-standing history of abnormal uterine bleeding underwent needle core biopsy, which showed a high-grade endometrial stromal sarcoma with a BCOR translocation. In the months following her diagnosis, the patient underwent multiple cycles of chemotherapy along with radiation therapy, but had disease progression. She then presented with bilateral pleural effusions. Cytology from the pleural effusions showed single cells and three-dimensional clusters of spindle-shaped to epithelioid cells. The cell block showed many groups of the atypical cells. The histologic and immunophenotypic features were consistent with metastatic endometrial stromal sarcoma. Ten months after initial diagnosis and two months after positive pleural fluid cytology the patient was deceased. Malignant pleural fluids with sarcoma metastases are not common. Endometrial stromal sarcomas are infrequent malignancies and those with BCOR translocations are recently described with a small number of cases reported. Pleural fluid metastasis of high-grade endometrial stromal sarcoma with BCOR translocation has not, to our knowledge, been described in the literature. [ABSTRACT FROM AUTHOR]