ECP 2023 Abstracts

S280 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 which is taken by phagocytosis that is mostly seen in plasma cell neo- plasms or lymphoproliferative disorders. Methods: A 43-year-old man presented with a mass on his right shoulder. Imaging showed widespread lytic bone lesions. The results of serum protein electrophoresis were not yet known. Excisional biopsy of the mass was sent to our lab with the question of malignancy. Results: Microscopically, the mass revealed a diffuse neoplastic growth in corticomedullary area, consisting of atypical cells with plasmacy- toid morphology. Cells had rounded nuclei, coarse chromatin and large eosinophilic cytoplasm. Additionally, homogeneous eosinophilic mate- rial containing cells were noted among the tumour cells which was sus- picious of amyloid deposition. Immunohistochemically, the neoplastic cells were CD38 and CD56 positive, and Ki67 proliferation index was 30%. Eosinophilic material containing cells were strongly stained with Kappa and CD68. Lambda was broadly negative with the exception of only a few plasma cells. Histochemically, gentian violet and congo- red staining were not compatible with amyloid. With these findings, the case was accepted as CSH accompanying plasma cell malignancy. Conclusion: CSH is an uncommon entity seen mostly in lymphopro- liferative disorders and plasma cell neoplasms but it can also be seen throughout the body (spleen, lymph nodes, bone marrow, kidney, gas- trointestinal tract, central nervous system, skin, kidney etc) in different circumstances. CSH is important to recognize as it may associated with increased mortality and worse prognosis. Recognition of this entity by pathologists and knowing that it may be mistaken with amyloid may help its differential diagnosis. E-PS-11-041 Hodgkin’s lymphoma with bone marrow involvement – study of immune escape markers T. Shet*, R. Johal, S. Epari, U. Sakhadeo *Tata Memorial Hospital, India Background & objectives: A small proportion of Hodgkin’s lym- phoma ( HL) present with hematologic symptoms of marrow involve- ment requiring a bone marrow biopsy. With immunotherapy being used in Hodgkin lymphoma understanding immune escape markers will help treat these patients better. Methods: We evaluated Immune escape markers in 7 cases of pri- mary bone HL(BHL) and 17 primary bone marrow presentation of HL(PMBHL) with 56 staging marrows involved by Hodgkin lymphoma (SBMHL). Stains for beta2 microglobulin, MHC class I, HLA class II and PD-L1 (Roche, SP142, monoclonal) were evaluated in Hodgkin / Reed Sternberg (HRS) cells and background in the three subsets. Results: MHC I correlated significantly with B2 microglobulin In HRS cells whereby 25/32 (78.1%) tumours with downregulated MHC I also had reduced B2 microglobulin. HLA II expression in HRS cells was negative or lost in 24 cases (44.6%). Expressions of beta2 microglob- ulin, MHC class I and HLA class II were significantly negative in BHL as compared to SBMHL or PBMHL. More cases of PBMHL appear to be positive for MHC-I and beta2 microglobulin as compared to SBMHL. PDL1 (SP142) was positive in 50/65(62.5%) samples. EBV was not associated with PD-L1. Univariate analysis revealed that tumours with > 90% HLA II expression in HRS cells showed favour- able prognosis. Conclusion: Besides HLA II expression, complete response on PET scan and histological pattern were significant for both overall survival (OS) and disease free survival (DFS) while in addition EBV negativity was adverse for OS. Patient with diffuse sclerotic pattern and nodular fibrohistiocytic pattern of marrow involvement had poorer survival. A unique pattern of Immune escape markers was seen in BHL, PMBHL and SBMHL and knowledge of these markers could help understand options for immunotherapy in these patients. Funding: Intramural funding from Tata Memorial Hospital E-PS-11-042 Smouldering systemic mastocytosis with the development of strik- ing osteosclerosis S. Stojnev*, M. Krstic, A. Ristic Petrovic, I. Conic, I. Petkovic, B. Lilic, M. Jevtic, M. Vucic *University Clinical Centre Nis, Medical Faculty University Nis, Serbia Background & objectives: Mastocytosis is a rare disorder caused by the clonal proliferation of neoplastic mast cells and their accumulation in tissues. In systemic mastocytosis, various organs can be affected, including the skeletal system. Bone involvement usually leads to osteo- porosis and pathological fractures. Methods: We present a case of a sixty-year-old male patient with macular skin rash, episodes of hypotension, and organomegaly who was diagnosed with systemic mastocytosis (SM) based on bone marrow (BM) biopsy findings. The patient was closely monitored and treated with H1-antagonists for 18 months. Clinical progression ensued, but BM examination showed no signs of associated myeloid or lymphoid neoplasm. Results: The initial diagnostic BM biopsy revealed remarkable histo- logic alterations: myeloid spaces were occupied by dense, granuloma- like aggregates of spindled and ovoid mast cells with paratrabecular and perivascular distribution. Neoplastic mast cells comprised more than 50% of total cellularity and showed typical immunophenotype with positive immunohistochemical expression of CD117, CD25, and CD30. Somatic point mutation of KIT D816V was confirmed. After the patient started to deteriorate clinically and developed leukocytosis and elevation of serum alkaline phosphatase, a novel BM biopsy was obtained. Examination revealed mast cell infiltration associated with prominent, diffuse osteosclerosis. Expanded bony trabeculae caused stenosis and subtotal obliteration of marrow spaces. Conclusion: SM represents a major diagnostic challenge since the release of mast cell mediators causes a myriad of manifestations. Skel- etal involvement is rare and underlined by the interaction of mast cells with bone remodelling but prominent osteosclerosis is rare. Sclerotic lesions of the bone, especially in the axial skeleton, can lead to mis- diagnosis of metastatic cancer of Paget’s disease. This case depicts an unusual evolution of SM and highlights the importance of including SM in diagnostic protocols of sclerotic bone lesions. E-PS-11-043 Plasmablastic lymphoma: multicentre case series from Turkey C.S. Sucubulak*, B. Altuntaş Keskin, E. Mercan Demirtaş, A.Y. Altay, M. Ayyildiz Mercan, A.S. Demiröz, G. Yegen, H. Aki, F. Öz Puyan *İstanbul University-Cerrahpasa, Cerrahpasa Medical Faculty, Pathol- ogy Department, Turkey Background & objectives: Plasmablastic lymphoma(PBL) is a rare lymphoma that is mostly found in HIV-infected patients and infiltrates mostly oral cavity. Different extranodal site involvement can also be encountered. We have limited sources of PBL in the literature because of its rare nature. Methods: We retrospectively reviewed 32 PBL cases from 3 tertiary consulting centres in Turkey (n=32). The cases were evaluated by their clinical findings, associated viral exposure (HIV and EBV), immuno- histochemistry, histology, and site of involvement. Results: The mean age of the patients was 59 (range=22-85). 23 patients were male, and 9 were female. 16 patients presented with nodal disease, 20 of them had extranodal involvement. Extranodal infiltration sites were stomach, gingiva, nasopharynx, maxilla, femur, epidural cavity, soft tissue, and hypophysis. HIV status of 9 patients were known and 3 of them were positive. Our immunohistochemistry results showed CD20(-)(26/30), CD138/CD38(+)(15/17), MUM1(+)