ECP 2023 Abstracts

S278 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 LCA, C-KIT, CD25, and CD43; while negative for synaptophysin, CK, CD2, CD3, CD4, CD20, DOG-1, MPO, and CD123. Sanger sequenc- ing confirmed D816V KIT mutation. The patient then revealed itchy macular lesions over the axillary region. Bone marrow biopsy revealed approximately 8-10 % mast cells confirmed by CKIT. Serum tryptase levels were elevated (72.9μg/l). Treatment with midostaurin demon- strated good response so far. Conclusion: Systemic mastocytosis (SM) is a disease with a heteroge- neous presentation and gastric involvement is frequently affected with rather vague and nonspecific clinical manifestations, making the diag- nosis of gastric mastocytosis particularly difficult. Histologically, sys- temic mastocytosis can be easily confused with other conditions such as inflammatory bowel disease or eosinophilic colitis. The differential diagnosis is easily resolved with appropriate immunohistochemical stains and molecular study. Thereby, high index of suspicion is essen- tial to correctly recognize this rare entity and improve quality of life. E-PS-11-033 Fibrin-associated diffuse large B-cell lymphoma (FA-DLBCL) in a renal cyst C. Padrão*, J. Derman, P. Gaulard, M. Mamodaly, E. Poullot *Hospital Prof. Dr. Fernando Fonseca, Portugal Background & objectives: An incidental suspect renal cyst (Bosniak IV) was discovered in a 72 years-old man in the context of follow-up from prostate cancer operated in July 2022. He underwent surgical removal of the cyst in December 2022. Methods: Macroscopically the lesion measured 7 x 6.5 x 6 cm. It was a well-defined, encapsulated nodular lesion. In section it was composed of a fibrous dense capsule, and a multiloculated cavitary with a gelatinous and liquid yellowish citric content. The cavitary lesion was totally included after one first microscopic evaluation that did not show any neoplastic evidence. Results: On histopathology, the capsule was fibrous and did not show any epithelial lining, with some lymphoid infiltrate and lymphoid fol- licles. In a small percentage of the slides in the subcapsular area, there were clusters of medium to large atypical lymphoid cells with abundant clear cytoplasm and a voluminous nucleus, often with a prominent central nucleolus. Numerous figures of mitosis and apoptosis were observed. The content of the cavity was composed of fibrin with some atypical cells detected within. Immunohistochemistry showed that the neoplastic cells were CD20+, PAX5+, CD5-, CD10-, Bcl6+, MUM1+, Bcl2+, cMYC-, CD30+(>80%), EBV+(latency type-3 profile), HHV8-, ALK1-, p53 wildtype. The proliferation index (Ki67) was high (80-90%). Conclusion: These findings are consistent with the diagnosis of Fibrin- associated diffuse large B-cell lymphoma in a renal pseudo-cyst. Fibrin-associated diffuse large B-cell lymphoma was previously con- sidered a subtype of diffuse large B-cell lymphoma associated with chronic inflammation (DLBCL-CI) but is now recognised as an entity in the WHO Classification of Haematolymphoid Tumours 5th edition and ICC classification. Pathologists should be aware of this entity and differentiate it from conventional DLBCL and DLBCL-CI to avoid overtreatment since it has a better prognosis. E-PS-11-034 Granulomatous slack skin with lung and oesophagus involvement? A case report and molecular analysis F. Pereira*, G. Esteves, J. Costa Rosa, J. Cabeçadas, M. Cravo, I. Barbosa, A. Robson *Hospital Professor Doutor Fernando Fonseca, Portugal Background & objectives: Granulomatous slack skin (GSS) is a rare subtype of mycosis fungoides (MF), and few cases have been known to spread to the blood, lymph nodes, or viscera. We present a case with early dissemination to the lung. Methods: A 27-year-old female, previously healthy, presented with vulvar and intergluteal firm oedema and groin-skin hardening, associated with scattered disseminated scaly patches for one year, without pain or pruritus. She also complained of mild fatigue and breathlessness on moderate exer- tion. There were no B symptoms. The patient underwent blood tests, skin biopsies and computed tomography (CT) scan. Results: The skin biopsy showed a mildly atypical T-cell lymphoid infiltrate involving the dermis/hypodermis, with focal epidermotropism, associated with a granulomatous infiltrate dominated by multinucleated giant cells. Elastophagocytosis was seen. The CT scan revealed bilateral ground-glass lung nodular opacities. Positron Emission Tomography showed increased signal in skin and subcutis around buttocks, inguinal and mediastinal lymph nodes, and lobes of the lungs. The lung biopsy confirmed a dense T-cell infiltrate with numerous multinucleated giant cells. Subsequently, oesophageal involvement was also observed follow- ing biopsy. Molecular analyses demonstrated identical T-cell clones in the skin and lung. After six cycles of chemotherapy/localized external radio- therapy, the patient had stable lung disease and a partial skin response. Conclusion: A preferred diagnosis of GSS with systemic spread was made based on clinical/histological/molecular findings, after consider- ing granulomatous MF and peripheral T-cell lymphoma, NOS. This case highlights the frequent diagnostic difficulty in distinguishing GSS from an inflammatory granulomatous dermatitis. Pulmonary and oesophagus involvement is rare in GSS and the simultaneous pres- entation of characteristic skin GSS with systemic disease poses an additional classification challenge. E-PS-11-035 Primary follicular lymphoma limited to the endometrium in a 55-year-old woman Z. Prouzová*, M. Kalinová, M. Mrhalová *Department of Pathology, 3rd Faculty of Medicine, Charles Uni- versity and University Hospital Královské Vinohrady, Department of Pathology, 1st Faculty of Medicine, Charles University and General University Hospital in Prague, Czech Republic Background & objectives: A 55-year-old woman with no history of malignancy was indicated for hysterectomy for significant postmenopau- sal bleeding. Methods: The material from the hysterectomy was processed in a standard way, formalin fixed and paraffin embedded tissue blocks were used for standard histological examination. Further immunohistochem- ical evaluations were used for detailed investigations of the process and, moreover, fluorescent in situ hybridisation (FISH) was added. Results: The endometrium was atrophic, infiltrated by the nodular lym- phoid infiltrate composed of medium-sized centrocytoid cells with mini- mal admixture of large centroblasts. Immunohistochemical examination revealed a CD20 positive B-lymphocyte population with co-expression of CD10 and BCL2 markers. FISH revealed characteristic abberation t(14;18) and, thus, confirmed the diagnosis of follicular lymphoma. Conclusion: The patient underwent a detailed haematological exami- nation and since she did not show signs of generalization of the disease, a "watch and wait" approach was chosen for the patient. She has now been relapse-free for 4 years. Primary lymphomas of the female genital tract are rare (0.2-1.1% of all extranodal lymphomas), moreover follicular lymphomas are unique, especially when they are not generalized. Treatment depends on the extent of the underlying disease, in our case, hysterectomy was a cura- tive therapeutic procedure. E-PS-11-036 Grading of myelofibrosis post-polycythemia vera and post- essen- tial thrombocythemia G. Sahraoui*, N. Kouki, R. Doghri, N. Boujelbene, I. Abbes, L. Charfi, K. Mrad *Salah Azaiez Institute, Tunisia Background & objectives: Polycythemia vera (PV) and essen- tial thrombocythemia (ET) are among the most common chronic