individuals are also infected with EBV and therefore evidence malignant cells that express products of this virus such as EBER1/2 nuclear RNA's. Cases associated with HIV/AIDS test positive for antibodies directed against this virus. (PEL occurs in the absence of HHV-8 and HIV, although this is rare.) Individuals with PEL that is associated with cirrosis due to hepatitis evidence positive serum tests for the hepatitis virus B antigen (HBsAg) or one of the various tests for hepatitis C antigen. Extracavitary PEL is diagnosed based on findings that their mass lesions contain the same or very similar types of malignant cells and the same set of blood and serum findings as those that are found in cavitary PEL. KSHV/HHV8-negative primary effusion lymphoma Effusion-based lymphoma, KSHV/HHV8-negative (also termed Type II PEL) has been described by some researchers. These cases closely resemble KSHV/HHV8-positive (also termed Type I PEL) but have yet to be defined by the World Health Organization (2017). Compared to Type I PEL, Type II PEL occurs more often in older individuals, is less often associated with EBV, and more often afflicts individuals who lack evidence of being immunocompromised. That is, the majority of HHV-8-negative EBL cases do not evidence a potentially PEL causative agent, such as HIV, EBV, HCV, or iatrogenic immunodeficiency, except for old age and, in 20% to 40% of cases, the presence of hepatitis C virus infection. Type II PEL also tends to involve malignant plasmablasts, anaplastic cells, and/or Reed-Sternberg-like cells that have somewhat different expression patters of protein markers (e.g. the malignant cells in Type II PEL frequently express CD20 but often do not express CD30) and gene abnormalities (e.g. the malignant cells in Type II PEL more commonly evidence rearrangements in their Myc, BCL2, and BCL6 genes) than the malignant cells in Type I PEL. The response to treatment and prognosis of Type II PEL is poor but may be somewhat better than the treatment-responsiveness and prognosis of Type I PEL. One factor that appears to improve the treatment of Type II PEL is the addition of rituximab (a monoclonal antibody directed against and killing CD20-bearing cell) to the intensive chemotherapy regimens used to treat Type I PEL: the malignant cells in Type II PEL commonly express CD20 whereas the malignant cells in Type I PEL rarely express this cell surface marker. However, there are several cases of KSHV/HHV8-negative EBL that presented with pericardial effusions