Persistent Unilateral Pleural Effusion with Chimeric Antigen Receptor T-cell Infiltration in Primary Mediastinal Large B-cell Lymphoma

Pleural effusion following chimeric antigen receptor (CAR) T-cell therapy is typically transient, bilateral, and associated with cytokine release syndrome (CRS). We herein report persistent unilateral massive pleural effusion with CAR T-cell infiltration in a 34-year-old man with refractory primary mediastinal large B-cell lymphoma involving pleural lesions treated with axicabtagene ciloleucel. Flow cytometry confirmed CAR T-cell infiltration into the pleural fluid. Although temporarily improved by corticosteroids, the effusion persisted for several months but eventually resolved spontaneously. Physicians should consider CAR T-cell infiltration in persistent unilateral pleural effusion after CAR T-cell therapy, emphasizing the importance of flow cytometry for the diagnosis and potential spontaneous resolution without corticosteroids.