Plasmablastic Richter Transformation of Chronic Lymphocytic Leukemia With Aberrant Epithelial Marker Expression Presenting as a Pleural Effusion: A Diagnostic Challenge

Richter transformation (RT) is a well‐known complication of chronic lymphocytic leukemia (CLL), and it is usually characterized by high‐grade transformation to diffuse large B‐cell lymphoma or, less commonly, to classic Hodgkin lymphoma. Rare reports describe RT presenting as plasmablastic lymphoma or myeloma. In this scenario, complete clinicopathological evaluation is critical to correctly classify the atypical transformation, and demonstration of a clonal relationship with precursor CLL is essential to confirm RT. Herein, we present a case of CLL with plasmablastic RT diagnosed on pleural effusion. The rarity of this phenomenon, compounded by aberrant expression of markers of epithelial differentiation, posed a significant diagnostic challenge. The unusual presentation in our case emphasizes the need for a comprehensive approach integrating clinical, morphologic, phenotypic, and molecular data to avoid misclassification and to guide appropriate clinical management.