ECP 2023 Abstracts

S378 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 characterized by a relatively good prognosis. Any type of RCC can undergo sarcomatoid differentiation, being most common in clear cell renal cell carcinomas (CCRCC). Methods: We present a 75 year old male with severe loss of weight in the last 2 months who shows radiologically a 16 centimetres heteroge- neous tumour on the left kidney. In macroscopy the tumour shows an irregular aspect, 15 centimetres in its maximum axis, with yellowish colour that invades the adjacent perirenal fat tissue. Results: Histological examination shows a biphasic tumour formed on one hand by uniform nests of big cells with clear cytoplasm, perinu- clear halo and very low or inexistent mitotic activity. The other com- ponent, which is the majority of the tumour, is formed by irregular spindle cells distributed in a stream or framework pattern with nuclear pleomorphism and high mitotic activity. There is necrosis associated in 40% of the mass. Both areas show common positive inmunostaining for CD117, CK7 and CKAE1/AE3. Conclusion: Chromophobe renal cell carcinomas are tumours who have a very good prognosis. We report an unusual CRCC with sarcomatoid transformation which greatly decreases survival. The common positive stainings supports the possibility that both areas have the same origin. Three months after the diagnosis the patient presents radiological dis- tant metastases and overall worsening. E-PS-24-046 Aquaporins expression in renal cell carcinomas: diagnostic and potential prognostic implications S. Marletta*, A. Caliò, F. Comper, F.M. Martelli, L. Stefanizzi, L. Marcolini, M. Brunelli, G. Martignoni *Department of Diagnostic and Public Health, Section of Pathology, University of Verona, Department of Pathology, Pederzoli Hospital, Peschiera del Garda, Italy Background & objectives: The ongoing evolution of renal cell carci- noma classification advocates for the identification of novel diagnostic and predictive markers. Aquaporins (AQPs) are a class of channels physiologically regulating cellular water flow, whose role in renal neo- plasms has not been studied yet. Methods: In the present study, we sought to evaluate in a wide series of renal neoplasms the diagnostic and prognostic value of the immuno- histochemical expression of the aquaporins molecules AQP-1, AQP-2, and AQP-3. Three-hundred fifty cases were retrieved, including both common and much rarer entities, according to the recently released 2022 WHO classification, and fourteen tissue microarrays (TMAs) were built. Results: While all major types of renal cell neoplasm failed to express AQP-3, immunolabeling for AQP-1, normally found in proximal renal tubules, was mainly observed in clear cell (101/102, 99%) and papil- lary renal cell carcinoma (27/41, 66%). Conversely, all chromophobe renal cell carcinomas (55/55, 100%) and oncocytomas (92/92, 100%) expressed AQP-2, physiologically found in distal renal tubules. Regard- ing rarer histotypes, both fumarate hydratase-deficient and succinate dehydrogenase-deficient renal cell carcinomas were only immunola- beled for AQP-2. Concerning prognostic variables, the coexpression of AQP-1 and AQP-2 significantly correlated with a high nucleolar grade (G3-G4) in both clear cell (p < 0.04) and papillary renal cell carcinomas (p < 0.02). Conclusion: In this study we have demonstrated that AQP-1 and AQP-2 can be added in a diagnostic panel as an additional tool to distinguish clear cell/papillary renal cell carcinoma from oncocytoma/ chromophobe renal cell carcinoma, and fumarate hydratase-deficient (just labelling for AQP-2) from papillary renal cell carcinomas (usually staining for both), which represent their main differential diagnosis. Furthermore, higher AQP-1 and AQP-2 expression in clear cell and papillary tumours showing aggressive nucleolar features (G3-G4) sug- gests a possible prognostic role. E-PS-24-047 PD-L1 expression in two molecular subtypes of muscle invasive urothelial bladder carcinoma S. Mašic*, S. Trifunović, V. Vrbić, M. Knežević, R. Terlević, B. Krušlin, M. Ulamec *Clinical Department of Pathology and Cytology, University Hospital Center Sestre milosrdnice, Zagreb, Croatia Background & objectives: Muscle invasive urothelial bladder car- cinoma (MIBC) represents aggressive neoplasm with high mortality. Two main MIBC molecular subtypes with diverse molecular signa- ture are familiar. Recently, immunotherapy with immune checkpoint inhibitors and PD-L1 expression level as potential response predictor was introduced. Methods: Forty FFPI tissue samples of patients with MIBC were stained for HE and immunohistochemistry. GATA-3 and CK5/6 expres- sion was used to roughly determine molecular subtype (basal or lumi- nal). PD-L1 expression (SP 142) was interpreted as the percentage of positive peri- and intratumoral staining of tumour microenvironment immune cells and correlated with molecular subtype. Results were considered statistically significant when p<0.05. Results: Cases showing CK5/6 positive and GATA-3 negative reaction were classified as basal subtype, while CK 5/6 negative and GATA-3 positive as luminal subtype. PD- L1 positive expression was observed in 28 samples based on cutoff value of 1%. Statistically significant posi- tive correlation was determined between PD-L1 expression and basal subtype, while negative correlation was established between PD-L1 and the luminal subtype. Conclusion: Results of our study demonstrated possible immuno- histochemistry algorithm in molecular subtype assessment, as well as correlation of PD-L1 expression with basal immunophenotype, which could suggest patients’ positive response to anti- PD- L1 immunotherapy and more successful management of this group of patients. However, to confirm the connection between basal molecular subtype and PD-L1 expression, we believe further research and molecular analysis should be conducted on larger patient cohort. E-PS-24-048 A rare localisation for intravascular papillary endothelial hyper- plasia (Masson’s tumour) A.S. Mavuş*, S.G. Barut *Haseki Education and Research Hospital, Turkey Background & objectives: Intravascular papillary endothelial hyper- plasia (Masson’s tumour) is a vascular proliferation that considered as a benign and non-neoplastic proliferation. Herein, we represent our rare case of Masson‘s tumour in spermatocele cyst wall in an 76 years-old male patient. Methods: The patient underwent operation for scrotal swelling with preoperative diagnosis of spermatocele. The operational material is 8x7x5.5 tan- brown cystic flat tissue. Hematoxylin- Eosin slides were mostly consist of hyalinized fibrous cystic tissue surrounded by the mesothelial layer and adipose tissue. In one slide, we saw papillary pro- liferation within and at the borders of an empty space inside cyst wall. Results: On higher magnification the cells were monotonous, with round and small nuclei. We didn’t notice any atypia or mitotic figures. Benign and malignant mesothelial proliferation and vascular lesions were in our differential diagnosis. We ordered some immunohisto- chemical stains for differential diagnosis. None of the mesothelial markers (CK5/6, Calretinin) were positive in our case and all the