ECP 2023 Abstracts

S384 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 the left kidney was found through ultrasonography exam. Following further clinical and paraclinical examinations, a partial nephrectomy was performed. The specimen was sent to the Pathology Department. Results: Gross examination was specific. A well-circumscribed tumour, with a tan-brown appearance, measuring 2.5 cm (mean size range: 2.8 cm) was identified. Microscopically, the tumour was surrounded by a fibrous capsule and presented a follicular architecture composed of micro and macrofollicles with a “colloid-like” appearance. The cells had amphophilic cytoplasm, with round nuclei and uniform chromatin. Unobtrusive nucle- oli, classified as ISUP/WHO grade 2 were observed. Focci of haemorrhage were present. On immunohistochemistry, tumour cells expressed PAX 8, CK 7, CK19, and were negative for TTF-1, CD10 and AMACR, proving their renal origin and excluding a metastatic thyroid carcinoma. The final diagnosis was Thyroid-like follicular carcinoma of the kidney, stage pT1a. Conclusion: Thyroid-like follicular renal cell carcinoma is a distinct histological subtype of renal cell carcinoma with only a few cases described in the literature (<50). This case illustrates the heterogene- ity of this rare renal tumour in terms of morphology and immunophe- notype. The tumour shares morphological similarities with primary thyroid follicular carcinoma, but immunohistochemistry is mandatory for establishing a correct diagnosis. E-PS-24-068 Expression of programmed death ligand -1 and mismatch repair status in renal cell carcinomas M. Rao*, P. Elhence, A. Nalwa, G.R. Choudhary *Department of Pathology & Lab Medicine, AIIMS, Jodhpur, India Background & objectives: Programmed death ligand -1 (PD-L1) is a co-regulatory molecule which suppresses the local immunity. Mis- match repair (MMR) deficiency has been implicated in the pathogen- esis of many malignancies and has been reported to influence response to anti PD-L1 targeted therapy. Methods: Expression of PD-L1 and MLH1, MSH2, MSH6 and PMS2 was assessed by immunohistochemistry (IHC) on 60 resected cases of renal cell carcinomas (RCCs). Results: Mismatch repair deficiency was noted in 6 cases (10% of the cases), of which five cases showed isolated loss of MLH-1, and one case showed combined loss of MSH2 and MSH6. PD-L1 expression was noted in 12 cases (20%). No significant relation was seen between MMR status and PD-L1 expression in RCCs. Conclusion: Approximately one fifth of RCC cases express PD-L1. However, mismatch repair deficiency is noted in only 10% of RCCs. More studies on a larger sample size are required to study relation between MMR status and PD-L1 expression in RCCs. Funding: Institutional Intramural Research Grant E-PS-24-069 Prostatic cystadenocarcinoma presenting as large pelvic cystic lesions – report of two cases F. Rosa*, J. Ferreira, F. Santos *Instituto Português de Oncologia de Lisboa Francisco Gentil, Portugal Background & objectives: Prostatic cystadenocarcinomas (PC) are exceedingly rare tumours mostly presenting as large pelvic cystic lesions (PCL). Imaging studies often fail to determine their anatomic origin and biopsies are frequently non-diagnostic, rendering pre-oper- ative diagnosis exceptionally challenging. Methods: We describe two cases of PC presenting as massive PCL without unequivocal continuity with the prostatic gland, according to pre-operative imaging studies and intra-operative findings. The literature was reviewed. Results: Case 1 refers to a 78-year-old man presenting with a 15,5 cm multilocular PCL. Case 2 refers to a 70-year-old man with a 21,5 cm unilocular PCL. Both had elevated serum PSA and prostatic lesions classified as PiRADS 5 and 4. In case 1, fine-needle aspiration was performed, and the cystic fluid revealed high PSA levels. In case 2, no biopsy or aspiration were performed. Radiologically and intra-opera- tively, unequivocal prostatic origin was not established. Both PCL were excised without radical prostatectomy. Morphologically, tumours had thick fibrous walls with intracystic papillary formations composed of ductal adenocarcinoma. Neoplastic cells were immunoreactive for PSA and NKX3.1 and negative for p63 and 34βE12. Conclusion: PC may present as multilocular or unilocular PCL, some- times lacking unequivocal continuity with the prostate. Association with a suspicious prostatic lesion or known prostatic adenocarcinoma, elevated serum PSA levels and elevated PSA in the cystic fluid may raise concern for this diagnosis. Accounting for the lack of a well- defined histologic spectrum of cystic prostatic lesions, this report raises awareness for this rare and pre-operatively challenging diagnosis. E-PS-24-070 A recently described entity: papillary renal neoplasm with reverse polarity D. Sá*, F.S. Vieira, S. Neves, F.E. Costa, J.R. Vizcaíno *Centro Hospitalar Universitário de Santo António, Portugal Background & objectives: Papillary renal neoplasmwith reverse polarity (PRNRP) was first described in 2019 by Al-Obaidy KI et al. They reported eighteen cases of a distinct subset of papillary renal tumours composed of cells with eosinophilic cytoplasm and apically located nuclei. Methods: We herein report a case of an 81-year-old man who was submitted to a renal ultrasound due to lower urinary tract symptoms. The ultrasound and subsequent CT scan revealed a renal nodule in the lower pole of the kidney measuring 1,8 cm and 1,6 cm, respectively. To remove this lesion, a partial nephrectomy was performed. Results: We received a partial nephrectomy specimen almost totally occupied by a tumour measuring 2,4 cm in greatest dimension, well delineated from the adjacent parenchyma and with a solid and tan cut surface. Histologic examination showed a well delineated neoplasia composed of papillae with thin fibrovascular cores covered by cuboi- dal to columnar cells with granular eosinophilic cytoplasm and apically located and regular nuclei without conspicuous nucleoli (grade 1 WHO/ ISUP). Some oedematous papillae were also seen. Immunohistochem- istry revealed expression of CK7 and GATA3 in the neoplastic cell with negativity for AMACR. Idylla® PCR molecular testing revealed a KRAS missense mutation involving c.35G>T resulting in p.G12V. Conclusion: Papillary renal neoplasm with reverse polarity is described in the WHO classification of tumour as a distinct pattern of papillary renal cell carcinoma. However, these tumours typically have a small size, low pathological stage and an indolent behaviour with no recurrences, metastasis, and disease-related deaths. Furthermore, KRAS mutations are frequent as opposed to 7, 17 and Y chromosomal anomalies, which are rare. For these reasons, recent studies suggest that this tumour should be separated from the papillary renal cell carcinoma. E-PS-24-071 Renal myopericytoma – report of a very rare case and review of the literature D. Sá*, G. Carrola, F.S. Vieira, F.E. Costa, J.R. Vizcaíno *Centro Hospitalar Universitário de Santo António, Portugal Background & objectives: Myopericytoma is a distinctive perivas- cular myoid neoplasm. It typically occurs in the skin and soft tissues and is extremely rare in visceral organs, with only 12 cases previously reported in the kidney, to our knowledge. Methods: We herein report a case of a 69-year-old woman with sarcoido- sis that presented with fever of unknown origin. She was submitted to a CT scan that revealed a renal mass in the middle third of the left kidney measuring 2,8cm suggestive of a renal cell carcinoma. To remove this lesion, a partial nephrectomy was performed.