Recognizing Fluid Overload‐Associated Large B‐Cell Lymphoma on Effusion Cytology: Two Illustrative Cases

Fluid overload-associated large B-cell lymphoma (FO-LBCL) is a distinct entity introduced in the 5th edition of the WHO Classification of Hematolymphoid Tumors (2022). It denotes a large B-cell lymphoma confined to one or more serous cavities as effusions, without a solid or nodal mass, in the absence of KSHV/HHV8 (and largely EBV) infection, arising in patients with fluid-overload states. It was previously reported under descriptive terms such as "HHV8-negative primary effusion lymphoma-like lymphoma." We describe two cases illustrating the WHO-HAEM5 diagnostic criteria and the diagnostic and prognostic workup of this entity.