ECP 2023 Abstracts

S270 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 arising in ovarian mature cystic teratoma was rendered, supported by immunohistochemistry, highlighting GFAP-positive glial component with coarse processes and NeuN-positive neurons. CD34, BRAF and IDH1 immunostains were negative in the neoplastic cells. Additionally, in view of the presence of reactive lymphoid infiltrate in the glial tissue, teratoma associated anti-NMDAR encephalitis might be considered. However, this is a clinical diagnosis and our patient did not have neurological symptoms. Conclusion: Ganglioglioma of CNS is a low-grade indolent tumour. However, considering its rarity in the ovary, the behaviour and progno- sis is difficult to determine and our patient is under close follow-up. To our knowledge, this case represents the second report of ganglioglioma arising in ovarian teratoma. E-PS-11 | E-Posters Haematopathology E-PS-11-001 Differential diagnosis in a rare spleen mass: inflammatory pseu- dotumour (inflammatory myofibroblastic tumour) versus inflam- matory pseudotumour like dendritic cell sarcoma B. Altuntaş Keskin*, A.S. Demiröz, T. Elverdi, H. Aki *Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty, Pathol- ogy Department, Turkey Background & objectives: Lesions that cause a spleen mass are usu- ally haemangioma, lymphoma, and angiosarcomas. Inflammatory pseudotumor is one of the rarely encountered lesions in the spleen. Dendritic cell sarcomas are much rarer. Both lesions are problematic in radiological and histological differential diagnosis. Methods: We present a rare case of a 70-year-old male patient admit- ted to the emergency department with mucosal bleeding and a spleen mass. On imaging, no hepatomegaly, lymphadenomegaly was detected. Total splenectomy was performed. The differential diagnosis included granulomatous lesions, angiosarcoma, sclerosing angiomatoid nodular transformation, splenic hamartoma, inflammatory pseudotumor (IPT) and inflammatory pseudotumor like dendritic cell sarcoma. Results: Histopathological examination revealed a well-delimited, off- white elastic mass, consisting of spindle cells intertwined with inflam- matory cells (histiocytes, lymphocytes, plasma cells, multi-nucleated giant cells). There was no necrosis. Dystrophic calcification was rarely present. No microorganisms were monitored with EZN or PAS dyes. Immunohistochemically, infiltration usually consists of positive cells for Vimentin, CD68, SMA, CD31, and negative cells for CD23, CD30, CD34, S100, ALK, CD1a, CD8, and also lymphocytes showing various B and T cell markers were abundant. Unlike inflammatory pseudotu- mor observed in other regions, EBER positivity can be seen in IPT of the spleen and inflammatory pseudotumor like dendritic cell Sarcoma. Conclusion: The rarity of these lesions and the difficulty in distinguish- ing them from other tumours of aggressive character require a multidis- ciplinary approach to ensure accurate diagnosis and optimal manage- ment. Although it is difficult to make a differential diagnosis in these two entities, both lesions are diagnosed and treated with surgery. Close follow-up is recommended especially for IPT-DCS because of the risk of local recurrence and metastasis. Our patient has been followed up without recurrence for 16 months after surgery. E-PS-11-002 Atypical monomorphic epitheliotropic intestinal T-cell lymphoma with brain invasion: a case report A. Arackal*, C. Murga-Zamalloa *Department of Pathology, University of Illinois at Chicago, USA Background & objectives: Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) is a rare, incidental primary intestinal T-cell lymphoma. Poor prognosis and high mortality rate are due to delayed diagnosis and lack of targeted therapy. Distinctive histopathological features have been described to have prognostic implication. Methods: A 66-year-old Cantonese-speaking male presented with abdominal pain. Further clinical investigation prompted an emer- gent partial ileectomy for small bowel perforation. Microscopically, pleomorphic atypical lymphocytes effaced the intestinal architecture. Positivity for CD3, CD8, CD56, c-MYC, TCR gamma/delta, and TIA- 1, with aberrant loss of CD5 supported MEITL. CHOP regimen was initiated. Brain parenchymal lesions were eventually identified and biopsied, confirming metastatic MEITL. Results: MEITL represents less than 5% of gastrointestinal tract lymphomas and is predominantly seen in South American and Asian countries. Other T-cell neoplastic proliferations, such as Enteropathy- associated T-cell lymphoma (EATL), should be excluded. Histologi- cally, MEITL is characterized by epitheliotropism, with monomorphic atypical T-cell lymphocytes that express CD56, CD8, and TCR gamma/ delta. Recently, an atypical variant has been described and is charac- terized by pleomorphic morphology, increased frequency of c-MYC amplification, and lower overall survival rates. Extradigestive/extran- odal involvement is commonly detected in the lung or liver, and exten- sion of MEITL into the brain parenchyma is rarely reported. Conclusion: In summary, MEITL is a primary intestinal T-cell lym- phoma with an aggressive clinical course and is rarely identified in North America. Recognition of variant morphological presentations is critical to establish the diagnosis, allowing for prompt and aggressive chemo- therapy. Further studies can better quantify the prognostic implications of immunohistochemical and molecular characteristics for MEITL. E-PS-11-003 Necrotising lymphadenitis (Kikuchi disease) (NEL) may be induced by endoplasmic reticulum stress S. Asano*, K. Yamazaki, H. Yuko, S. Kawana, H. Sato, M. Kashimura, H. Naito, Y. Sogame, K. Shikano *Iwaki City Medical Center, Japan Background & objectives: We examined immunohistochemical analysis and electron microscope of NEL in detail and found aggregates (tubulo- reticular structure) within the expanded ER, as well as concentric changes of the ER, which led us to further investigate ER stress in more detail. Methods: Data from 70 NELs were collected between 1989 and 2016. Lymph node samples were fixed in 2.5%-glutaraldehyde for electron microscopy (EM). For immunohistochemical analysis (IHC), formalin- fixed paraffin-embedded tissue sections were performed using an auto- mated staining machine; anti-GRP78 and anti-CHOP antibodies were used to examine ER stress and ER stress responses. Results: Tubular structures (TRS) were often observed within the expanded endoplasmic reticulum within microvessels, lymphocytes, and plasmacytoid dendritic cells, and SARC bodies were also observed. Strongly GRP78-positive cells, an endoplasmic reticulum chaperone molecule, and CHOP-positive cells, a pre-apoptotic factor, were also frequently observed in the focal areas. Conclusion: TRSs in the endoplasmic reticulum are unfolded proteins (UPs), which induce ER stress that leads to activation of stress sensors and massive mobilization of the chaperone molecule GRP78. However, when ER stress is strong and lasts longer, CHOP-positive cells appear and induce apoptosis, suggesting that apoptosis in this disease is induced by ER stress. E-PS-11-004 Castleman disease: multicentre case series from Turkey M. Ayyildiz Mercan*, E. Mercan Demirtaş, B. Altuntaş Keskin, A.Y. Altay, A.S. Demiröz, G. Yegen, H. Aki, F. Öz Puyan *Trakya University Medical Faculty, Pathology Department, Turkey Background & objectives: Castleman disease (CD) is a rare lym- phoproliferative disorder divided into subtypes with different aetiologies,