According to the WHO classification, PEL is defined as a large B-cell lymphoma that typically lacks expression of pan-B-cell markers (e.g., CD19, CD20, CD79a) although it often expresses CD45, CD138, MUM1, and EMA, and may aberrantly express T-cell markers such as CD3 and CD4 (48); A definitive diagnosis of PEL requires conclusive evidence of KSHV/HHV-8 infection, which is present in all cases; approximately 60%–80% of these are co-infected with EBV. This evidence concerns the gene CD4 and primary effusion lymphoma.