ECP 2023 Abstracts

S323 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 on tubulitis score [5 leukocytes per tubular cross section (32.4%)] and cortical inflammatory infiltrate [<!- -=25% (44.1%) and -->25% (55.9%)]. Mean follow-up time was 19.8 months. Renal recovery based on serum creatinine reduction levels, was 76.25%, consistent with the literature. The analysis of tubule-interstitial parameters compared with renal recovery rate, showed that patients with >5 inflammatory cells/tubular cross section and/or >25% inter- stitial inflammatory infiltrate and/or tubular destruction, significantly improved renal function (p=0.027, 0.05 and 0.041, respectively). Conclusion: The histological parameters analysed as tubulitis score, cortical inflammatory infiltrate percentage and tubular destruction dem- onstrated an independent and statistically significant association with renal recovery, without association to other variables such as acute tubular necrosis or additional glomerular pathology. These results high- light the importance of renal biopsy in ATIN to stablish a histological activity index, nevertheless future studies with larger sample sizes will be necessary to evaluate the reproducibility of these results. E-PS-16-016 Morphology and clinical presentation of small vessel vasculitides involving the kidney M. Životic*, G. Nikolić, A. Mioljević, P. Ratković, R. Naumović, A. Kezić, M. Radović, D. Paripović, G. Miloševski Lomić, N. Stajić, J. Putnik, D. Dunđerović, S. Radojević Škodrić *Institute of Pathology, Serbia Background & objectives: Pauci-immune small vessels vasculitides in kidney, could be divided into ANCA associated vasculitides (AAV) and non-ANCA associated vasculitides (NAAV). Our aim was to compare clinical and pathohistological characteristics of small vessel vascu- litides in kidneys of patients with AAV and NAAV. Methods: We performed a retrospective analysis of kidney biopsies, diagnosed between 2000-2020, at Institute for Pathology Faculty of Medicine University of Belgrade. Overall, 157 kidney biopsies with pauci-immune small vessels vasulitides were examined (79 patients with AAV and 78 patients with NAAV). Clinical data collected from medical records, and pathohistological parameters were examined and compared between the AAV and NAAV patients. Results: ANCA positive patients were significantly older (55.5±17.6 years) than ANCA negative (45±18.1 years) patients (p<0.001), and they also had significantly higher frequency of glomeruli involved by crescent formations (≈40%) compared to patients with non-ANCA vas- culitides (≈30%), p=0.012. Moreover, ANCA positive patients had higher frequency of chronic lesions such as interstitial fibrosis, tubular atrophy and glomerular sclerosis. Laboratory parameters were high in both groups, without significant difference. Clinically assessed BVAS score was similar in both investigated groups and did not show any significant difference. Conclusion: Patients with ANCA positive renal vasculitis are sig- nificantly older and have higher frequency of chronic glomerular and tubulointerstitial lesion, while laboratory and clinical parameters are not significantly different between ANCA positive and ANCA nega- tive patients. Funding: The study was supported by the Ministry of Education, Sci- ence and Technological Development of the Republic of Serbia. E-PS-16-017 Oxford classification (MEST-C score) - IgA nephropathy and Henoch Schoenlein pupura: similarity and difference? M. Životic*, G. Nikolić, A. Mioljević, V. Brković, A. Janković, S. Radojević Škodrić *Institute of Pathology, Serbia Background & objectives: We conducted a retrospective study, in order to assess potential clinical and morphological differences (assessed by MEST-C score), between IgA nephropathy (IgAN) and Henoch Schoenlein purpura (HSP). Methods: The study included patients with IgAN (n=67) and HSP (n=28) diagnosed at the Institute of Pathology, Medical Faculty, Bel- grade, Serbia. Clinical patient’s data (gender, age, haematuria, protein- uria and disease duration before biopsy) and pathohistological MEST-C score were analysed and compared between IgAN and HSP. Results: Patients diagnosed with IgAN were significantly older (33±17.9 years) than those with HSP (15±10.3 years). Higher serum creatinine values were observed in HSP (356.5±1071.1 μmol/l) com- pared to IgAN (117.4±73.6 μmol/l). The majority of patients with IgAN and all patients with HSP had diffuse glomerular mesangial hypercellularity. Endocapillary hypercellularity is observed in 6/67 IgAN and in 13/28 HSP patients. Segmental glomerular sclerosis was detected in more than a half of IgAN cases, while only a quar- ter of HSP exhibited these changes. Tubular atrophy and interstitial fibrosis were not observed in HSP, while 13/67 patients with IgAN had this lesion. Crescents formations were detected in 3 HSP and 15 IgAN patients. Conclusion: Active glomerular lesions are characteristics of HSP, while chronic parameters are frequently observed in IgAN patients who are generally older than HSP group. Funding: This work was supported by the Ministry of Education, Sci- ence and Technological Development of the Republic of Serbia. E-PS-17 | E-Posters Neuropathology E-PS-17-001 Bithalamic diffuse midline glioma H3K27-altered harbouring con- comitant EGFR and HIST1H3B mutation: a case report M.L. Abascal Camacho*, C. Vieru, A.J. Van der Biezen, M.N. Villca Huayta, E. Carceller Ortega, C. Garrido Ortega, F.J. Díaz Crespo, F. Arias *Hospital General Universitario Gregorio Marañón, Spain Background & objectives: Concomitant EGFR and H3mutations in diffuse midline glioma H3K27altered are extremely rare, with only 5 cases reported in the literature to date. We present a new case to expand our understanding of this pathology. Methods: A 4year-old boy, presented with tremor in the upper extremi- ties. Magnetic resonance imaging (MRI) revealed a diffuse supratento- rial tumour, centred in the midline with bitalamic involvement and right hemispheric extension. The mass was hypointense on T1 and isointense to hyperintense on fluid-attenuated inversion recovery images. The patient underwent stereotactic biopsy. Results: Histopathological evaluation revealed a diffuse glial neoplasm with high cellularity. Tumour cells displayed oval morphology, with hyperchromatic, irregular nuclei and sparse mitotic activity. Microvas- cular proliferation and necrosis were absent. Immunohistochemistry revealed strong nuclear immunoreactivity with H3K27M and P53, with complete loss of H3K27me3 in tumour cells. Ki67 index was approximately 20%. Next-generation sequencing detected mutations in HIST1H3-H3K27 (c.83A>T, p.Lys28met), EGFR (c.1793G>T, pGly- 598Val) and TP53 (c.524G>A, pAr175His). MGMT promoter methyl- ation was not present. DNA methylation analysis classified this tumour as a paediatric-type diffuse high-grade glioma-H3K27 altered, subtype EGFR altered. The patient received radiotherapy, chemotherapy, and immunotherapy treatment (Erlotinib) with poor response. Currently, the patient is receiving palliative care. Conclusion: DMG-H3K27 altered are characterized by the loss of H2K27me3. The WHO classification of 2021 recognizes four sub- types based on molecular alterations. The concurrent presence of H3K27 and EGFR mutations, leads to the loss H3K27me3, potentially resulting in the recognition of a fifth DMG-H3K27 altered subtype in the future. These tumours are extremely rare with limited treatment