Diagnostic Usefulness of Cell Block Samples in Fluid Overload-Associated Large B-Cell Lymphoma

Fluid overload-associated B-cell lymphoma (FO-LBCL) is a B-cell neoplasm that presents as serous effusions without detectable tumor masses and Kaposi sarcoma-associated herpesvirus (KSHV)/human herpesvirus 8 (HHV8) infection. Here, we report a case of an 81-year-old female patient with FO-LBCL (Stage IVA) who presented with pericardial and pleural effusions. The patient had no underlying medical condition that could lead to fluid overload. Cytological examination of both effusions revealed medium- to large-sized lymphoid cells with high nucleocytoplasmic ratios, irregular nuclei, dense chromatin, prominent nucleoli, mitotic figures, basophilic cytoplasm, and lymphoglandular bodies. A cell block of the pleural fluid effusion showed that atypical lymphoid cells were positive for CD20 and CD79a, and negative for CD3, KSHV/HHV-8, and Epstein-Barr virus. The Ki-67 labeling index was 95%. The patient underwent systemic chemotherapy and achieved complete remission without pleural or pericardial recurrence during the 3-year follow-up period. As FO-LBCL is diagnosed based on cytological material, together with clinical and imaging findings, immunohistochemical analysis of the cell block is useful for confirming the diagnosis and selecting tailored therapies.