ECP 2023 Abstracts

S376 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 associated outcome data represent an ideal source for developing AI systems that can better predict cancer aggressiveness than the Gleason score. E-PS-24-038 Clinical and pathological correlation in Erdheim Chester disease - a case report A. Georgescu*, T. Georgescu, S. Barbu, L. Petrescu, F. Pop *Department of Pathology, "Carol Davila" University of Medicine and Pharmacy Bucharest, Department of Pathology, Nephrology Clinical Hospital "Dr. Carol Davila", Bucharest, Romania Background & objectives: Erdheim-Chester disease is a histiocytic proliferation, which was first described in 1930, but which was only recently recognized as being a neoplasm. Accurate diagnosis requires a characteristic radiological aspect, which is supported by the per- inephric soft tissue biopsy. Methods: We report the case of a 47–year-old male, who presented to the Nephrology department with altered kidney function of unknown aetiology. Upon CT, a circumferential thickening of the perinephric fat, suggestive for the “hair kidney sign” was observed. Subsequently a PET-CT revealed symmetrical osteosclerosis of long bones and a perinephric biopsy was performed in order to establish the diagnosis. Results: Four core needle biopsies were received in the Pathology Department of the Nephrology Clinical Hospital “Dr. Carol Davila” Bucharest, three of which revealed an infiltration of the soft tissue with foamy macrophages and discrete histiocytes. Additionally, a mixed inflammatory infiltrate composed of lymphocytes and plasma cells, embedded in a fibrotic stroma was noticed. Immunohistochemical stains were performed and revealed that the histiocytic infiltrate was diffusely positive for CD68, CD163 and FXIIIa. No immunoreactivity towards CD1a was observed. The proliferation index was extremely low, of approximately 2%. BRAFV600E stain revealed diffuse strong cytoplasmic positivity of the proliferated histiocytes, and further molecular tests have confirmed the presence of the mutation. Conclusion: In conclusion, Erdheim-Chester disease requires a specific imagistic and pathological finding in order to be accurately diagnosed. Rarely, Erdheim-Chester disease can present with renal dysfunction secondary to ureteral compression, although more commonly the skin lesions and the haematological affliction usually precipitate the rec- ognition of this rare multisystemic disease. Our case highlights the importance of accurately recognizing the characteristic findings, which will consequently result in a multidisciplinary therapeutic approach. A favourable outcome can be achieved after BRAF or MEK inhibitors. E-PS-24-039 Solitary fibrous tumours of the genitourinary tract – report of two cases in rare locations J. Lobo*, M.A. Morini, B. Zein-Sabatto, S. Harada, V. Dal Zotto, C. Magi-Galluzzi *Portuguese Oncology Institute Porto, Portugal Background & objectives: Solitary fibrous tumours (SFT) arising in the genitourinary (GU) tract are rare. Differential diagnosis with other more common spindle cell tumours is challenging, especially in the context of small biopsies. Methods: We report two cases of SFT of the GU tract (involving semi- nal vesicle and spermatic cord), including morphology, immunophe- notype and molecular analysis. Results: Case #1 corresponded to a 40-year-old male presenting with haematospermia. Imaging revealed a 2 cm seminal vesicle nodule. Case #2 corresponded to a 48-year-old male presenting with scrotal enlarge- ment. Imaging revealed a 9 cm mass arising from the spermatic cord. Both cases showed a bland spindle cell proliferation with alternating cellularity, collagen deposition and thin-walled branching vessels. No necrosis, high mitotic index or pleomorphism were seen. Both cases were diffusely positive for STAT6/CD34. The seminal vesicle SFT was originally diagnosed in a pre-surgical biopsy; NGS confirmed NAB2-STAT6 fusion. MDM2 FISH was negative on the spermatic cord tumour excluding liposarcoma. Patients are alive without disease at 6 months/14 years after diagnosis. Conclusion: SFT should be included in the differential of spindle cell lesions of the GU tract. STAT6 IHC (strong nuclear expression) is a good surrogate marker for the NAB2-STAT6 fusion characteristic of SFT. While most tumours are indolent, 10-30% behave aggressively; outcome can be predicted based on available risk stratification models combining size and histopathological features (pleomorphism, mitotic index, necrosis). E-PS-24-040 Primary renal Ewing sarcoma: report of two cases, including one with an exceedingly rare EWSR1-ETV4 fusion J. Lobo*, R. Ahmed, B. Zein-Sabatto, T. Winokur, S. Wei, S. Harada, C. Magi-Galluzzi *Portuguese Oncology Institute Porto, Portugal Background & objectives: Ewing sarcoma (ES) of the kidney is exceedingly rare, with approximately 300 cases described in literature, the majority as case reports. Current challenges include differential diagnosis with other small blue round cell tumours with implications for treatment/prognosis. Methods: We report two cases of primary renal ES, including immu- nophenotype and molecular analysis. Results: Two female patients, aged 28/32 years, presented with abdomi- nal complaints. Each nephrectomy specimen revealed a 15cm mass with necrosis, extending into perinephric fat, renal sinus/vein, and involving the adrenal gland in one case. Tumour cells were small and ovoid/spin- dled. The differential diagnosis included Wilms tumour, desmoplastic small round cell tumour, rhabdomyosarcoma, synovial sarcoma, lym- phoma, melanoma and neuroendocrine carcinoma as well as recently described ES variants. A panel of immunohistochemical markers, includ- ing pancytokeratins, PAX8, WT1, muscle/melanocytic markers and CD45 was performed; both tumours were only positive for CD99, FLI1 and synaptophysin. EWSR1-FLI1 fusion was detected (by FISH and RT-qPCR) in one case and EWSR1-ETV4 fusion (by NGS) in the other. Conclusion: Accurate diagnosis of ES is important to select appropri- ate chemotherapy regimen. Molecular testing is critical to confirm the diagnosis. While approximately 90-95% of ES show a EWSR1-FLI1 fusion, EWSR1-ETV4 fusion has been described in rare isolated case reports, none primary in the kidney. ES with unusual fusion partners may have a predilection for extraskeletal sites. Additional studies are needed to assess the potential prognostic value of ETV4 gene partner. E-PS-24-041 Cystic trophoblastic tumour of the testis: report of two cases and utility of miR-371a-3p testing J. Lobo*, N. Tavares, D. Barros-Silva, A. Rosinha, A. Morais, C. Jerón- imo, Â. Rodrigues, R. Henrique *Portuguese Oncology Institute Porto, Portugal Background & objectives: Cystic trophoblastic tumour (CTT) of the testis is an infrequent and under-recognized entity, often focal and admixed with mature teratoma in post-chemotherapy retroperitoneal lymph-node dissection (pcRPLND) specimens. Its pathogenesis is still poorly understood. Methods: We report two cases of CTT, one in the context of pcRPLND and the other in a post-chemotherapy primary testicular tumour. We provide histopathological description, immunohistochemistry study and clinicopathological annotation. Additionally, we submitted the CTT component to miR-371a-3p RT-qPCR testing, comparing with