Biopsy-proven inflammatory pulmonary opacities mimicking lymphoma relapse after CD19 CAR-T-cell therapy.

Pulmonary lesions that newly emerge after chimeric antigen receptor T-cell therapy may raise immediate concern for lymphoma relapse, especially when they occur at sites of prior disease involvement. We report a patient with refractory diffuse large B-cell lymphoma who developed newly apparent or re-enlarged FDG-avid pulmonary opacities four months after axicabtagene ciloleucel infusion. The lesions appeared at or near prior pulmonary lymphoma-suspected sites, strongly suggesting recurrence. However, transbronchial lung biopsy showed organizing pneumonia-like inflammatory changes with Masson bodies, CD3-positive T-cell infiltration, and no evidence of lymphoma involvement by multiple B-cell markers. Because the patient remained clinically stable and relapse was not supported histologically, systemic corticosteroids and salvage chemotherapy were withheld. The biopsied lesion and the remaining pulmonary opacities regressed spontaneously during follow-up, and complete remission was maintained. This case illustrates that organizing pneumonia-like inflammatory lesions may arise at prior lymphoma-suspected pulmonary sites after CAR-T-cell therapy and closely mimic pulmonary relapse on FDG-PET/CT. When new FDG-avid pulmonary lesions arise after CAR-T-cell therapy, particularly at prior lymphoma sites, tissue confirmation is essential to avoid misdiagnosis and unnecessary treatment escalation.