ECP 2023 Abstracts

S381 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-24-056 Low-grade oncocytic tumour of the kidney: report of two cases K. Palamaris*, A. Stofas, A. Patereli, D. Goutas, N. Katsoulas, A. Georgiou, H. Gakiopoulou, P. Korkolopoulou *First Department of Pathology, National and Kapodistrian University of Athens School of Medicine, Greece Background & objectives: Low-grade Oncocytic Tumour (LOT) of kid- ney is a newly renal tumour entity that carries good prognosis as compared with other renal cell neoplasms, shows oncocytic cell-like morphology and is characterized by a CK7-positive/CD117-negative immunoprofile. Methods: We report 2 cases of LOT of a 64-year-old male with a history of polycystic kidney disease/chronic renal failure with a tumour in his left kidney and of a 75-year-old male with a tumour in his left kidney. Grossly, both tumours were well circumscribed, with solid brown cut surface, measuring 6 and 3,1 cm in the greatest dimension respectively. Results: On microscopy, both tumours showed a predominantly solid and nested growth pattern. The tumour cells had abundant eosinophilic cytoplasm, with bland low-grade nuclei. Necrosis was not observed. On immunohistochemistry, the tumour cells were strongly and diffusely positive for CK7, while being negative for CD117. PAX8, CK7 and CK8/18 were also positive in both neoplasms, while all tumour cells were negative for Vimentin, CD10 και CAIX. Based on these features, a diagnosis of low-grade oncocytic tumour of kidney was given. Conclusion: Low-grade oncocytic tumour of the kidney is a new cat- egory in the family of renal cell tumours that should be distinguished from other renal epithelial cell tumours showing eosinophilic cytoplasm, as the former is an indolent neoplasm and carries good prognosis. E-PS-24-057 Renal oncocytomas: morphological and immunophenotypical vari- ability in central scar M. Pané-Foix*, D. Fernández-Calvo, A. Domingo Rubio, N. Espejo- Herrera, E. Condom, M.R. Taco, M. Gomà Gallego, M.Á. López, A. Vidal *Pathology Department - Hospital Universitari de Bellvitge, Spain Background & objectives: Renal oncocytomas (RO) usually pre- sent areas of scarring. Cellular groups adjacent/enclosed within often exhibit a different morphology from the rest of the tumour. The aim of this work is to verify these morphological changes and to characterize its immunophenotype. Methods: Cases of RO diagnosed between 2016-2022 (N=103) were reviewed and those in which an area of central scar was observed (N=20) were selected. The presence of morphological changes in cell groups encompassed in the scar was verified and an immunohisto- chemical panel was applied: CK7, Vimentin, Racemasa (AMACR), Carbonic Anhydrase IX (CAIX), Napsin, CD117. Results: Twenty cases that contained, at least focally, areas of tubular morphology within the fibrous scar were identified. These areas, unlike the rest of the tumour, showed a different morphology characterised by tubular or cord-like architectural patterns, cells with ovoid or spin- dle-shaped nuclei, clear cytoplasm, and absence of typical oncocytic features. Immunohistochemically they displayed intense positivity for CK7 (in 20/20 cases) and Vimentin (20/20 cases) and tended to lose CD117 expression (negative in 19/20 cases); weaker and more irregular positivity for AMACR (19/20 cases) and Napsin (19/20 cases). CAIX was variably and focally positive (9/20 cases). Conclusion: Scar areas in RO usually encompass cellular groups with morphology and immunohistochemical profile different from the rest of the tumour. These features could be tentatively interpreted as adap- tive changes to hypoxia and/or, considering positivity for AMACR and Napsin A, as a form of nephrogenic metaplasia. It is important to know its existence to avoid, especially in limited samples, confusing OR with other histological types or collision tumours. E-PS-24-058 Differential diagnostics of urothelial lesions via immunohistochemi- cal method V. Pechnikova*, L. Mikhaleva, O. Vasyukova, A. Konyukova, K. Maslen- kina, A. Birukov, K. Midiber, R. Vandysheva, Z. Gioeva, L. Kakturskiy *Avtsyn Research Institute of Human Morphology of Federal State Budgetary Scientific Institution "Petrovsky National Research Centre of Surgery", Russia Background & objectives: To develop a panel of immunohistochem- ical (IHC) antibodies to simplify the differential diagnosis between urothelial lesions (reactive atypia of bladder vs. urothelial dysplasia). Methods: The material of the study (histological slides) was obtained from patients with urothelial lesions: 10 cases with verified reactive bladder atypia and 10 cases with urothelial dysplasia. IHC staining was performed using CK7, CK20, Ki-67, p53, CD44, Bcl-2, HER2, Uroplakin III, FGFR3, PTEN and GATA3 antibodies. IHC scoring was completed using the HistoScore (HScore) method. Results: The study revealed significant differences in HScore values between the two study groups for CK20 (p=0.021), p53 (p=0.018), Bcl-2 (p=0.025), GATA3 (p<0.001), HER2 (p<0.001) and Uroplakin III ( p<0.001). Expression of CK20, Bcl-2, GATA3, HER2, and Uroplakin III is significantly more pronounced in the reactive atypia group; on the contrary, dysplasia is characterized by a pronounced reaction with the p53 marker. Conclusion: The resulting IHC panel of antibodies (CK20, p53, Bcl-2, GATA3, HER2, and Uroplakin III) will improve the differential diagno- sis of inflammatory and precancerous lesions for pathologists E-PS-24-059 Plasmacytoid variant of invasive urothelial bladder carcinoma: a case report T. Pikivača*, A. Zenko Sever, A. El-Saleh, A. Lukač *Clinical Department of Pathology and Cytology, University Hospital Centre Zagreb, Croatia Background & objectives: Plasmacytoid urothelial carcinoma of the urinary bladder is a rare and an aggressive variant of high-grade urothelial carcinoma. It is characterized by somatic mutations of CDH1 leading to frequent loss of E-cadherin expression. Methods: A 56-year-old man was diagnosed with invasive urothe- lial carcinoma (pT2) after he underwent transurethral resection of the urinary bladder tumour. The radiological staging of the disease did not show any signs of an extended disease. After neoadjuvant chemo- therapy, radical cystectomy with bilateral pelvic lymphadenectomy and resection of the distal portion of the ureters was performed. Results: Grossly, there was poorly circumscribed thickened area near the trigonum and at the ostia of the ureters. Histologically, the tumour was composed of discohesive plasmacytoid tumour cell aggregates, cords and individual cells, some of which resembled signet-ring cells. The tumour infiltrated the full thickness of the bladder wall, surround- ing fatty tissue, seminal vesicles, prostate, prostatic urethra, lympho- vascular spaces and the resection margin of the distal portion of the left ureter. There were metastasis in multiple regional lymph nodes. Immunohistochemically, tumour cells were diffusely CD138 positive with the loss of membranous E-cadherin expression. The patient was sent for re-staging, followed by a decision on further treatment. Conclusion: Awareness of plasmacytoid urothelial carcinoma´s unique morphology and immunohistochemical profile is important to avoid a potential misdiagnosis from its mimics. The discohesive tumour cells can spread extensively along tissue planes and peritoneal sur- faces. Compared with conventional urothelial carcinoma, plasmacytoid urothelial carcinomas have a greater chance for higher-stage disease, surgical margin positivity and metastasis at presentation. It is important to make accurate distinction especially on the initial transurethral resec- tion specimens because of the therapeutic and prognostic implications.