ALK and primary effusion lymphoma: Some entities, such as plasmablastic lymphoma, primary effusion lymphoma, anaplastic lymphoma kinase (ALK)-positive large B-cell lymphoma, and human herpes virus-8 (HHV-8)-positive DLBCL- not otherwise specified (NOS) show reduced expression of markers of B-cell differentiation and upregulation of plasma-cell differentiation antigens.