ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 treatment. In those submitted to surgical resection (11;20%), final diagnosis was concordant with biopsy diagnosis in 8 (73%) cases; and in 3 (27%) cases, it was included in the biopsy differential diagnosis. ISUP grade was upgraded from 2 to 4 in one case. Sev- enteen (30%) patients died, most (12;71%) from kidney cancer. Conclusion: Kidney tumour biopsy is of paramount importance in patient management. Our series highlights the two main clinical settings leading to kidney tumour biopsy in our institution, with distinct diagnosis challenges – small tumours treated by cryto- therapy or clinical follow-up, and aggressive tumours requiring histological subtype classification. It is also noteworthy the high concordance in the biopsy and surgical specimen diagnosis, as reported in the literature. PS-26-037 Caveolin-1 expression in tissue and cfDNA methylation status in semen plasma of patients with benign prostate hyperplasia and prostate cancer S. Mašić*, L. Škara, T. Vodopić, N. Sinčić, D. Tomas, B. Krušlin, M. Ulamec *Sestre milosrdnice University Hospital Centre, Ljudevit Jurak Clinical Department of Pathology and Cytology, Zagreb, Croatia Background & objectives: Prostate cancer (PCa) is the second most common malignancy and the fifth cause of death in male popula- tion. However, non- invasive and specific biomarker for distinguish- ing benign prostate hyperplasia (BPH) and prostate cancer is still not known. Methods: Eighty tissue samples of patients (40 with PCa, 40 with BPH) were stained for HE and immunohistochemistry. Caveolin-1 (CAV1) expression in BPH and PCa was scored according to stain- ing intensity and percentage of positive cells. Degree of cfDNA methylation as a potential biomarker for PCa was estimated in semen samples by pyrosequencing. Results were considered sta- tistically significant when p<0.05. Results: Statistically significant higher cytoplasmic CAV1 staining intensity score and staining proportion were observed in BPH stroma compared to PCa stroma. There was no epithelial reaction in both groups. Staining score did not correlate with Gleason grade group, nor with tPSA. In case of semen samples, cfDNA methylation mean of the first five CpGs was higher in BHP group while methylation of other CpGs and average methylation was similar in both groups. BHP cfDNA methylation median of 8 CpGs and average methylation was similar, difference between groups was ≤ 1%. Statistically significant degree of hypermetilated cfDNA for CAV1 only in CpG1 was observed in BPH patients compared to PCa patients. Conclusion: Caveolin-1 is a protein important for caveolae for- mation in plasma membrane invaginations. It’s functions include regulation of cell differentiation, apoptosis, cell proliferation, migration, angiogenesis, senescence, endocytosis and interaction with signalling molecules. The expression of this protein signifi- cantly differs in BPH and PCa tissue. As for cfDNA methylation, significant differences in DNA methylation of CpG1 between BPH and PCa were demonstrated. CAV1 is a potential non- invasive biomarker for distinguishing BPH and prostate cancer. PS-26-038 Low grade oncocytic renal tumour (LOT): clinicopathological characterization of 9 cases from a single cancer centre B. Xu*, A. Fawaz *Roswell Park Cancer Center, USA Background & objectives: Oncocytic renal neoplasms are heterogeneous group of tumours that can pose diagnostic challenge. Recently, a subset of renal oncocytic neoplasms is described as LOT. In this study, we further investigate the histomorphological characteristics and clinical outcome of LOT, retrospectively. Methods: Among 87 patients with low grade oncocytic renal neo- plasms, 9 cases of LOT were identified from pathology archive between year 2005-2021. All cases were confirmed by immu- nostains for CK7, CD117 and other relevant markers. The clin- icopathological characteristics features and follow up data were investigated. Results: Median age of patients is 83 years old with male to female ratio of 1:7. Grossly, the tumours are heterogeneous solid masses (2 with cystic changes). The median size of tumour is 2.65 cm. Histologically, tumours show solid compact nested, focal tubu- lar or trabecular patterns. Tumour cells are monomorphic bland with eosinophilic cytoplasm and uniformly round nuclei. Tumour nuclear grade is WHO/ISUP grade 2. All cases show strong CK7 positivity and negative for CD117, CAIX, CD10, AMACA and vimentin. All cases in our cohort demonstrate indolent behaviour and show no evidence of disease recurrence, progression or metas- tases during the follow-up period up to 82 months (median 13.5 months). Conclusion: LOT is an emerging entity with incidence of 10% among low grade ORN. It has unique morphologic and immuno- histochemical profiles that set them apart from oncocytoma and chromophobe renal cell carcinoma. LOT demonstrates indolent clinical behaviour. Future studies will be directed to understand molecular genetic profiles of LOT. PS-26-039 Implications of correlation between PBRM1 and PD-L1 expres- sion in renal cell carcinoma, clear cell type H. Hwang, G. Choe*, K.S. Lee *Seoul National University College of Medicine, Republic of Korea Background & objectives: Polybromo-1 (PBRM1) is the second most frequently altered gene after von Hippel-Lindau gene in clear cell renal cell carcinoma (ccRCC). PBRM1 alteration is reported as a significant barrier to immune checkpoint blockade response including anti-PD- L1target therapy. Methods: To identify the correlation between PBRM1 and PD-L1 expression in ccRCC, we analysed the loss of PBRM1 (A301- 591A; dilution: 1:250, Bethyl Laboratories, Montgomery, TX) expression and PD-L1 (22C3; pharmDx assay, Agilent, Santa Clara, CA) expression in a retrospective cohort of 526 surgically resected ccRCC in a single institute. Results: Based on a cut-off of the combined positive score (CPS) ≥1%, positive staining for PD-L1 was found in 139 (26.4%) cases. Loss of PBRM1 expression was observed in 205 (39.0%) cases. PD-L1 expression was positively associated with loss of PBRM1 expression (P<0.001) in ccRCC. Notably, among the ccRCC cases which expressed the PD-L1, loss of PBRM1 was identified in more than 50% of cases. In addition, loss of PBRM1 expression showed correlations with aggressive clinicopathological features including higher ISUP/WHO grade, high pT stage, angiolymphatic invasion, venous invasion, and tumour necrosis (P<0.05). Kaplan–Meier analysis indicated that loss of PBRM1 expression and PD-L1 expression was positively correlated with tumour recurrence. Conclusion: In ccRCC, previous clinical trials reported that there is no significant correlation between PD-L1 expression and anti-PD-L1 therapeutic effect. Our study showed that the loss S178