A rare case of primary effusion lymphoma in HIV negative patient: Diagnostic challenges and literature review.

We present a rare case of primary effusion lymphoma (PEL) in a 75 year old, HIV-negative male patient with multiple comorbidities. Imaging studies revealed a massive right pleural effusion and a significant lung collapse with multiple plural soft tissue nodules. Immediate thoracentesis was performed. Cytologic evaluation of the pleural fluid showed abnormally large cell with increased nuclear to cytoplasmic ratio, irregular nuclear contours and prominent nucleoli, with phenotypic expression of HHV-8, CD138, CD30, and MUM1 markers and negative staining for epithelial and mesothelial markers. PEL is a rare and aggressive large B-cell lymphoma often affecting immunocompromised adults and is mostly associated with human herpes virus 8/Kaposi sarcoma-associated herpes virus (HHV-8/KSHV). However, cases in immunocompetent elderly patients have been reported. The cytomorphologic features of PEL overlaps with those of aggressive lymphomas such as diffuse large B-cell lymphoma, plasmablastic lymphoma, and anaplastic large-cell lymphoma. Also, mesothelioma, metastatic carcinoma or melanoma should be considered in the differential diagnosis. Hence, PEL should be kept in mind in the diagnostic algorithm of cytological evaluation of serosal fluid not only in HIV positive patients but also HIV-negative elderly patients. In this report, we aim to highlight the cytologic and immunohistochemical staining pattern of this rare entity to increase awareness of this entity among cytopathologists.