ECP 2023 Abstracts

S371 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-24-017 Peroxidasine overexpression in intratumoral vessels and in proxi- mal tubular cells adjacent to clear cell renal cell carcinomas (CCRCC): a case series A.R. Coelho*, R. Silva, I. Alencastre, J. Reis Almeida, I. Brandão, J.P. Oliveira *Centro Hospitalar Universitário de São João, Porto, Portugal Background & objectives: Peroxidasine (PXDN) is an extracellular matrix protein with peroxidase activity important in the development of fibrosis. Its role in cancer is still not well established. We aimed to characterise PXDN expression in a series of oncocytoma and CCRCC. Methods: Ten cases of oncocytoma and twelve cases of CCRCC were retrieved from our hospital files between 2021 and 2022. Their clinico- pathological features and follow-up were reviewed. PXDN expression was analysed by immunohistochemistry in tumour and in non-neoplas- tic adjacent parenchyma (< 1cm), using a defined score established for intensity and extent of expression. Statistical analysis was performed using SPSS Statistics. Results: Both tumour types showed an expression of PXDN in >50% of tumoral cells with high intensity. However, the expression in intratumoral vessels showed a higher extent (p=0.030) and intensity (p<0.001) in CCRCC versus oncocytoma. The expression of PXDN in proximal tubular cells was more intense in non-neoplastic parenchyma adjacent to CCRCC (high intensity in 83,3% of cases) versus oncocy- toma (p=0.030). PXDN expression in distal tubules was similar in both groups, with a high intensity of expression. No relation between PXDN expression and grade or stage was found. There were no evidence of metastasis nor tumour related deaths. Conclusion: The literature suggests that in cancer, PXDN might be important for proliferation and invasion. Our results showed a signifi- cantly different pattern of expression in PXDN between CCRCC and oncocytoma, namely in intratumoral vessels and in proximal tubular cells of non-neoplastic adjacent parenchyma. Therefore, we hypoth- esise a potential role of PXDN in the angiogenesis of CCRCC and a potential paracrine effect in non-neoplastic parenchyma. Further stud- ies need to be performed to confirm these findings and explore their significance. E-PS-24-018 Utility of GCDFP15 as a marker of seminal epithelium in prostate biopsies M. Conde Ferreirós*, M.d.l.Á. Betancor Santos, M.J. Acuña Martínez, L.M. Liste Tizón, S. Abdulkader Sande, P. Mendez Pena, M.P. San Miguel Fraile, M.T. Dawid de Vera, J. González-Carreró Fojón, J.A. Ortiz-Rey *Hospital Álvaro Cunqueiro, Spain Background & objectives: The incidental presence of seminal vesicle epithelium in prostate needle biopsies may occasionally be misinter- preted as malignant because of architectural and cytologic features. We have analysed the utility of GCDFP15 as an immunohistochemical marker to confirm seminal epithelium. Methods: 22 prostate needle biopsies from 19 patients which inciden- tally contained seminal vesicle epithelium, 20 seminal vesicle sections coming from prostatectomy surgical specimens and three TMAs con- structed from 75 cases of prostatic adenocarcinoma Gleason≥8 were immunostained. Monoclonal antibodies anti GCDFP (Gross Cystic Disease Fluid Protein)-15 and PAX8 (as a positive control of seminal epithelium) and a multimer-based detection method were used. Results: GCDFP15 cytoplasmic immunoreactivity was intense in the 20 seminal vesicle surgical specimens, as well as in the seminal epi- thelium of the 22 prostate needle biopsies that contained it with focal or diffuse staining. GCDFP15 was expressed in 3 of the 75 samples of prostatic adenocarcinoma included in the TMAs: one intraductal carcinoma and two foci of normal prostatic epithelium. Sensitivity of GCDFP15 as a marker of seminal epithelium was 100% and specific- ity was 96%. PAX8 was positive, intense and diffusely, in all cases of seminal epithelium ( 20 samples of surgical specimens and 22 biopsies) being negative in benign or malignant prostate epithelium, with sensi- tivity and specificity=100%. Conclusion: The strong immunohistochemical expression of GCDFP15 aids to the identification of seminal vesicle epithelium in prostate biopsies. It is a sensitive marker but not completely specific (96%): GCDFP15 can be rarely positive in normal prostate epithelium and intraductal carcinoma of the prostate. The use of additional mark- ers, like PAX8, could be advisable to confirm accurately seminal epi- thelium. A possible application of our findings is that seminal vesicle tissue can serve as a positive control for the immunohistochemical staining of GCDFP15. E-PS-24-019 The reticulin pattern in renal neoplasias, the old new tool for dif- ferential diagnosis – a histochemical evaluation M. de Brito Pereira*, A.S. Carralas Antunes, M.E. Vitorino, K. Amaral Freitas, P. Fernandes, J. Palla Garcia, R. Ilgenfritz *CUF Descobertas Hospital, Portugal Background & objectives: Among the most frequent renal neoplastic entities, heterogeneity is expected and morphological overlap is com- mon. (1) Even with immunohistochemistry and other complementary evaluation, the diagnosis can be difficult. This study aims to evaluate reticulin stain as a diagnostic tool. Methods: We evaluated the reticulin pattern in 47 cases of the most common renal neoplasms [clear cell renal cell carcinoma (RCC) – 11 cases, papillary RCC – 13 cases, oncocytoma - 11 and chromophobe RCC – 12 cases]. Each case was randomly selected in two different institutions, one frag- ment was chosen and the reticulin staining was performed by auto- mated methods. Results: Among the clear cell renal cell carcinomas, a single cell pattern of staining in the periphery/fibrous areas was the most com- mon finding (10/11), among groups of cells, it varied from complete to incomplete bridging depending on morphologic patterns. In papillary carcinomas, 1-layer staining pattern in each side of the papillary pole, without any staining in micropapillary structures was observed (13/13), with occasional peri-macrophage staining. In 3 cases with reverse polarity, additional weak luminal staining was present. Regarding oncocytomas, a complete bridging pattern (1/2-layered) with irregular groups was observed, without perivascular reinforce- ment (11/11). Chromophobes presented perivascular reinforcement in rectilinear ves- sels, with incomplete to absent bridging in solid areas (12/12). Conclusion: In this study, significant differences in the reticulin pat- tern of each entity were observed. Although different morphologic patterns added some variation between cases, certain findings were common among almost all cases of the same entity. Further studies, with a higher sample and more entities, should be con- sidered in order to support the use of reticulin as a diagnostic tool simi- lar to its use in hepatic pathology (2) and sex cord stromal tumours (3). Funding: Partial funding by Roche Portugal E-PS-24-020 A rare disease series of 3 cases in testis: Mesothelioma M. Dicleli*, G. Türkcü, S. Özekinci *Cizre State Hospital, Turkey Background & objectives: Mesothelioma of tunica vaginalis testis (TVT) is a very rare and it has a poor prognosis. Mesotheliomas of