C80-27 From Effusion to Lymphoma: A Rare Case of Primary Pleural Diffuse Large B-cell Lymphoma

Abstract Introduction Primary pleural diffuse large B-cell lymphoma (DLBCL) is a rare form of extranodal lymphoma originating in the pleura, presenting as a lymphocyte-predominant exudative effusion without systemic involvement. While secondary involvement in DLBCL is not uncommon, primary pleural disease is rare, often reflecting aggressive disease behavior. We present a case of primary pleural DLBCL without prior history of lymphoma or known predisposing risk factors. Case Description 51-year-old female with hypertension and discoid lupus presented with acute dyspnea. She was hypertensive (BP 200/97 mmHg), tachypneic (29 breaths/min), and hypoxemic (SpO2 96% on 15L/min nonrebreather mask). Laboratory results were unremarkable except for elevated bicarbonate (32 mmol/L). CT chest revealed diffuse opacification of the left lung, a large left pleural effusion and a smaller right-sided effusion. Left-sided thoracentesis drained 1.5L of serosanguineous fluid; however, post-procedure imaging demonstrated persistent effusion. Pleural fluid was exudative, lymphocyte-predominant with protein 4.2 g/dL, LDH 6040 U/L, and glucose20 mg/dL. Gram stains and cultures were negative. Due to concerns for lupus pleuritis, solumedrol was initiated, however, studies revealed only positive ANA, with negative anti-dsDNA, anti-centromere, anti-CCP, anti-histone, and rheumatoid factor, making lupus-related serositis less likely. Despite corticosteroids, oxygen requirements increased, prompting repeat bilateral thoracenteses for symptomatic relief. Viral, fungal panels (HIV, EBV, and Coccidioides) and serum protein electrophoresis were negative. Pleural fluid cytology demonstrated large atypical lymphoid cells with prominent nucleoli and apoptosis. Immunohistochemistry showed CD20+, PAX5+, BCL-2+, BCL-6+, and MUM1+ expression, ruling out primary effusion lymphoma. FISH revealed loss of IGH and MALT1, confirming DLBCL-NOS, non-germinal center B-cell (non-GCB) subtype. Bone marrow biopsy and flow cytometry revealed normocellular marrow with no evidence of lymphoma. The patient was initiated on Pola-R-CHP chemotherapy, showed improved oxygenation after repeat thoracenteses, and was discharged with scheduled PET staging. Discussion Primary pleural DLBCL is a rare entity, with only isolated cases described in literature. Diagnosis requires excluding systemic lymphoma and other causes of exudative effusions including metastasis, autoimmune disease or infection. As illustrated in this case, patients typically present with dyspnea, large pleural effusions without a dominant mass and confirmed cytology and immunophenotyping. PET-CT is required for staging and detecting extranodal/marrow involvement. Primary pleural DLBCL should be considered in patients with unexplained, recurrent exudative effusions unresponsive to conventional therapy. The presence of pleural effusion is an adverse prognostic factor linked to higher relapse and poorer survival, especially in the non-GCB subtype. Hence prompt recognition and timely initiation of chemoimmunotherapy is crucial for improving outcomes. This abstract is funded by: None