Primary effusion anaplastic large cell lymphoma with indolent clinical course and IRF4/DUSP22 rearrangement: a case report expanding the spectrum of effusion-based lymphoma.

Effusion-based lymphomas arising from pleural cavities are mostly B cell lymphomas. Non-B cell origins are very rare. These non-B cell lymphomas are usually disseminated and aggressive, and their underlying genetic changes are indeterminate. Here, we reported the first case of primary effusion anaplastic large cell lymphoma (ALCL) with exclusive involvement of a single body cavity, indolent initial presentation, and IRF4/DUSP22 rearrangement. This 73-year-old man had been in his usual health until he presented with exertional dyspnea for 1 month. Physical examination and whole-body imaging indicated isolated left pleural effusion without lymphadenopathies or tumors. Thoracentesis revealed anaplastic large lymphoid cells that were CD30 + , CD3 - , CD8 + , TIA1 + , CD138 - , Epstein-Barr virus-encoded small RNA - , human herpesvirus 8 - , and ALK - . Fluorescence in situ hybridization exhibited IRF4/DUSP22 rearrangement. A primary effusion ALK-negative ALCL was diagnosed. There was no evident progression without chemotherapeutics until 4 months after the diagnosis. Our findings expanded the spectrum of effusion-based lymphoma. Recognition of this disease could prevent misdiagnosis and guide treatment strategies for patients.