This weakening is ascribed to KSHV/HHV8 infection that is commonly further promoted by concurrent human immunodeficiency virus (i.e. HIV) infection, prior organ transplantation, the decline in immunity that develops with aging, and/or cirrhosis of the liver due to hepatitis B or C virus. The plasmacytoid cells in PEL are also commonly infected with the Epstein-Barr virus (i.e. EBV). EBV is a known cause of various Epstein-Barr virus-associated lymphoproliferative diseases including various B-cell lymphomas. However, the role of this virus in the development of PEL is not clear, although some studies suggest that EBV infection cooperates with KSHV/HHV8 infection to promote the development and/or progression of this disease.Formally, PEL is defined by the World Health Organization, 2016 as a KSHV/HHV8-positive and KSHV/HHV8-driven large B-cell lymphoma. This lymphoma also belongs to a group of lymphoid neoplasms with plasmablastic differentiation that involve malignant plasmablasts but differ from PEL in the types of tissues where they accumulate, the gene abnormalities they carry, and/or the predisposing conditions involved in their development. More than 50, 30, and 60% of all PEL cases, respectively, develop in individuals who already have KSHV/HHV8-positive Kaposis sarcoma, human herpesvirus 8-associated multicentric Castleman disease, and/or (especially in HIV-positive individuals) evidence of bearing EBV-infected plasmablasts.Primary effussion lymphoma is an extremely aggressive cancer that is highly resistant to various chemotherapy treatments. It has carried a median survival time of ~5 months, with overall survival rates at 1, 3, and 5 year of only 30, 18, and 17%, respectively.
This is related to the fact that the symmetric group 
  
    
      
        
          
            S
          
          
            n
          
        
      
    
    {\displaystyle \mathrm {S} _{n}}
   is a solvable group for n ⩽ 4 and not solvable for n ⩾ 5.