Anaplastic Large Cell Lymphoma Manifesting as Pleural Effusion in a Patient with Long-Standing Eosinophilia

Anaplastic large cell lymphoma (ALCL) is a lymphoma of T-cell origin, characterized by the presence of large lymphoid cells with abundant cytoplasm and pleomorphic, often horseshoe-shaped nuclei (hallmark cells), as well as strong and uniform expression of cluster of differentiation (CD)30. Two distinct clinicopathologic categories of ALCL include primary cutaneous ALCL and systemic ALCL. Systemic ALCL is further classified into anaplastic lymphoma kinase (ALK)-positive, ALK-negative, and breast implant-associated ALCL. Most ALCLs occurring in adults are ALK negative and present in lymph nodes rather than extranodal sites.Primary diagnosis of ALCL in the pleural fluid is extremely rare, with no convincing recent reports available that are based in current understanding of this entity. Herein, we describe a well-characterized case of ALK-negative ALCL with no rearrangement but amplification of DUSP22/IRF4, diagnosed by cytologic examination of the pleural effusion in a 68-year-old white man with a 3-year history of unexplained eosinophilia and pulmonary infiltrates. Also, we present a review of the literature and discuss the current understanding of ALCL based on the 2016 revision of the World Health Organization (WHO) classification of lymphoid neoplasms.