ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Conclusion: The diagnosis of PPM can be challenging, especially in small samples, due to non-neoplastic mimickers such as reactive pericarditis with mesothelial hyperplasia. A through pathological exam, cemented by a targeted immunohistochemical panel, remains the cornerstone for establishing an accurate diagnosis . PPM carries a bleak prognosis, given its non-specific symptoms that produce an insidious progress, its difficult surgical management and its slight benefit from radiation and chemotherapy. E-PS-23-005 Intrathymic melanoma: report of two cases with a rare localization F. Fortarezza, F. Pezzuto*, F. Lunardi, V. Verzeletti, G. Cannone, M. Schiavon, F. Rea, F. Calabrese *University of Padova, Italy Background & objectives: Melanoma can have various visceral locali- zations with or without the presence of a known skin origin. Thymic localization represents an exceptional event with rare cases reported in the literature. Herein we describe two cases of intrathymic melanoma. Methods: All thymectomy cases performed in our centre over t he last 20 years were reviewed and two cases of melanoma were found. Both cases were reviewed by expert pathologists. An extensive immunohistochemical panel and molecular analyses were per formed to conf irm the diagnosis. Clinical-pathological data of the two patients were collected. Results: Case 1: A 53-year-old man accessed to the emergency room for dyspnoea and thoracic pain. The CT-scan showed a mass of the anterior mediastinum. A thymectomy was performed. Histological examination showed a neoplasm morphologically and immunohistochemically compatible with melanoma. Molecular examination showed no mutation of BRAF. Dermatological and gastrointestinal examination did not detect neither skin nor visceral melanoma. Case 2: A 62-year-old man with a history of cutaneous mela- noma showed a retrosternal mediastinal mass during radiologi- cal follow-up. A thymectomy was performed and a diagnosis of intrathymic metastasis of melanoma was made. The neoplasm harboured the same mutation of the primary cutaneous melanoma (BRAF V600E) and showed a high PD-L1 expression. Conclusion: Intrathymic localization of melanoma is an excep- tionally rare event. When intrathymic localization represents the onset of the disease (as in the case of the patient 1), it raises the question about the existence of the primary melanoma of the thy- mus or whether it is a metastasis from an occult skin melanoma. In-depth studies based on high throughput molecular investiga- tions are needed to answer these questions. E-PS-24 | E-Posters Uropathology E-PS-24-001 Pleomorphic adenoma with PLAG1 fusion presenting as an isolated kidney mass: report of a challenging case J. Lobo*, M. Rechsteiner, N.J. Rupp, H. Moch *IPO Porto, Portugal Background & objectives: Metastasizing pleomorphic adenoma is an infrequent diagnosis (81 cases described). Metastasizing pleomorphic adenoma involving the kidney is rare, with only eight cases disclosed until 2018. Presentation as a single incidental kidney mass is unusual. Methods: We herein report a case of a pleomorphic adenoma pre- senting as a kidney mass in a 43-year-old female, and discuss chal- lenges in differential diagnosis with primary renal tumours. Results: The tumour was low-grade and showed a triphasic pat- tern, with ductal epithelial cells (strongly staining for CK7 and pan-cytokeratins), myoepithelial cells (proved by co-expression of p63, GFAP, S100, Calponin and SMA) and myxoid/oedematous stroma. Next generation sequencing identified a PLAG1 fusion typical of pleomorphic adenoma (also confirmed by immunohisto- chemistry), and plasmacytoid features (frequently associated with PLAG fusions) were also present in our case. The diagnosis led to further clinical observation, and the patient referred that she had removed a pleomorphic adenoma of the parotid gland 36 years before, at age 12. Conclusion: The case highlights the relevance of carefully exam- ining the salivary glands and of exploring past medical history related to salivary gland disease (even decades before) when in the presence of myoepithelial differentiation, and underscores the usefulness of PLAG1 immunohistochemistry and molecular test- ing for diagnosis. Funding: H.M. receives a Swiss National Science Foundation grant (No. S-87701-03-01). E-PS-24-002 Malignant triton tumour of the kidney in a 57-year-old male: a case report A.C. Ablaza*, A. Llanes *Baguio General Hospital and Medical Center, Philippines Background & objectives: Preoperative diagnosis of malignant triton tumour (MTT) remains challenging as no specific imaging character- istics distinguish it from other sarcomas. The aim is to describe a rare case of MTT of the kidney and its diagnostic challenges and patient outcomes. Methods: Histopathologic examination and immunohistochemical staining with S-100, desmin, and myogenin were performed. Results: Gross examination showed a 16 x 12.5 x 12.5 cm, cream- white, fleshy mass almost replacing the entire kidney. Cut sections revealed whorled cut surfaces with areas of necrosis. Histologically, the tumour is composed of spindle shaped cells with pleomorphic, hyperchromatic nuclei with prominent nucleoli and pale wavy cytoplasm, reminiscent of their Schwann cell origin. Seen within the tumour are several rhabdomyoblasts having large eccentric nuclei with prominent nucleoli and abundant densely eosinophilic cytoplasm. The tumour cells stained focally positive for S-100, desmin, and myogenin, indicating Schwannian and skeletal muscle differentiation. Conclusion: MTT of the kidney is an exceptional occurrence and has a highly aggressive behaviour associated with rapid growth and propensity for early recurrence and metastasis. Preoperative diag- nosis of this tumour is difficult, thus highlighting the importance of histopathology and immunohistochemistry in the definitive diag- nosis. The optimal treatment strategy may depend on tumour char- acteristics and clinical presentation and should be individualized. E-PS-24-003 Glomangiomyoma of the kidney-case report of a rare subtype of glomus tumour with unusual location M. Chivu*, A. Muresan, A. Petrescu, L.E. Mitrache, M.G. Berdan *University Emergency Hospital Bucharest, Romania Background & objectives: Glomus tumours arising in the kidney represent rare benign lesions, with only a few cases described in the S349