Abstracts Clinical Lymphoma, Myeloma & Leukemia September 2023 S446 Mglow <1.7 mg/dL, normal 1.7 <2 mg/dL, Mghigh 2 mg/dL. Biologic analysis included cytokine analysis of pts from ZUMA-1 and scRNAseq of PBMC of 13 pts from the Mayo Clinic cohort, both before lymphodepletion (pre-CART) and at CART-peak. Results: The two groups had similar characteristics. In the ZUMA-1 cohort, there was a lower CRR in pts with hypomagnesemia compared to those with normal or high Mg (P=0.03). This translated into an inferior PFS (P=0.022) and OS (P=0.001). Similar results were observed in the Mayo Clinic cohort. Mg levels inversely correlated with the abundance of serum cytokines. Accordingly, a lower number of pts with Mglow experienced grade 3 CRS. Using CellChat analysis, we found that pts with Mghigh at pre-CART had a higher number of interactions between CD16 and CD14 monocytes and between these cells with CD4 and CD8 T cells. Similarly, CD8 T effector memory (TEM) cells strongly interacted with other immune cells. At CART-peak the same interactions decreased dramatically in pts with Mghigh, while there was a significant increase in the number and strength of interactions of CD4 TEM cells with CD8 T cells and monocytes, suggesting an antigen-restricted response. A transcription factors analysis identified enrichment for the methyltransferase KMT2A, SPI1, and the proto-oncogene MYC in Mglow pts. A ligand-receptor analysis confirmed a reduced interaction between multiple HLA subtypes-CD8 T cells with monocytes, CD4 and CD8 TEM cells in Mghigh pts. Conclusion: Hypomagnesemia is prognostic and associated with altered immune interactions in LBCL pts receiving CART cells, however whether optimizing Mg levels would improve CART efficacy remains unknown. Keywords: ABCL, large B-cell lymphoma, CART cells, single cell RNAsequencing, hypomagnesemia, immune response Indolent B-Cell Lymphoma IBCL-011 Castleman Disease: An Unusual Presentation of a Rare Disease Asmaa Mohsen MD1, Mohamed Elboghdady MD1, Walaa Ahmed Yusuf MD2, Elsherbiny S MD2, Maha M Amin professor2, Shaimaa El Ashwah assistant professor1, Yasmine Shaaban MD1 1Clinical Haematology Unit, Internal Medicine Department, Faculty of Medicine, Mansoura, Egypt. 2Pathology Department, Mansoura University Hospitals, Mansoura, Egypt Context: Castleman’s disease (CD) is a rare heterogeneous group of lymphoproliferative disorders characterized by angiofollicular lymph node hypertrophy. CD is divided into unicentric CD (UCD) and multicentric CD (MCD). Unicentric CD can be cured by excision surgery or radiotherapy, but it can be challenging to diagnose and differentiate from solid malignancies and other lymphomas. Objective: Here we report the clinicopathologic findings and treatment outcome of an unusual presentation of a young Egyptian gentleman diagnosed with UCD and describe his treatment journey. We hope that this report will aid in understanding the pathogenesis and prognosis of CD in this rare cohort of patients. Design and Methods: A case report which includes diagnostic history, physical examination, complete blood count, chemistry profile, virology, immune profile, tumor markers, and tissue biopsy, along with radiological follow-up. Main Outcome: The 28-yearold gentleman presented with a one-year history of undiagnosed fever and abdominal pain. Ultrasound scan showed a 5.6 cm gastric wall mass. A triphasic CT scan confirmed it as an upper abdominal 4.6 cm mass arising from the inner aspect of the posterior wall of the pyloric region, highly vascular at the periphery with nodal infiltration, which was highly suspicious of gastrointestinal stromal tumor (GIST). Endoscopic ultrasound was done to obtain a biopsy that was inconclusive for reactive tissue with a low KI index. A laparoscopic total excisional biopsy led to a diagnosis of CD (hyaline vascular type) with reactive hyperplasia of associated lymph nodes (LNs). Autoimmune disorders, overlapping IgG4-related disease, viral infection, thrombocytopenia, anasarca, fever, reticulin fibrosis, organomegaly (TAFRO) syndrome, and other malignancies were excluded. The patient was classified as having a UCD and was treated with total excision. Follow-up PET CT and CT scans showed complete resolution with no residual lesions, and the patient followup in the outpatient clinic was uneventful. Conclusion: UCD can sometimes be very challenging to diagnose and can be misdiagnosed as solid malignancy, especially with rare, atypical presentations. The curative role of surgery in UCD has dramatically improved the outcome of this rare cohort of patients. Keywords: IBCL, unicentric Castleman disease, excision, GIST, case IBCL-057 Incidence and Features of SARS‑CoV‑2 Breakthrough Infection in the Hematological Conditions After Tixagevimab‑Cilgavimab Prophylaxis Andrea Duminuco MD, Antonella Nardo MD, Alessandra Orofino MD, Giuliana Giunta MD, Concetta Conticello MD, Vittorio Del Fabro MD, Amalia Figuera MD, Annalisa Chiarenza MD, Giuseppe Milone MD, Salvatore Leotta MD, Alessandra Cupri MD, Marina Parisi MD, Elisa Mauro MD, Calogero Vetro MD, Francesco Di Raimondo MD, Alessandra Romano MD, Giuseppe A. Palumbo MD U.O.C. Hematology with BMT, A.O.U. Policlinico “G.Rodolico-San Marco”, Catania, Italy Context: Despite the development of anti-COVID-19 messenger RNA vaccines, several immunocompromised patients (above all affected by hematological disorders) were unable to produce antiSARS-CoV-2 spike antibodies in response to vaccination. In this context, preexposure prophylaxis with tixagevimab-cilgavimab (TIX-CIL), approved in 2022 by FSA and EMA, has resulted in an alternative strategy based on the promising results of the phase III PROVENT study. Objective and Design: This retrospective observational report aims to collect the clinical data of 202 patients affected by hematological diseases and treated in a single center with prophylactic therapy with TIX-CIL, evaluating the incidence of breakthrough infections and, in infected patients, the duration, the severity (potential reduction of severe forms) and the outcome.
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