- Histologically or cytologically proven NPC of an WHO grade, associated with EBV infection documented by the presence of EBER expression by in situ hybridization in the tumor. Positive EBER staining from another institution must be confirmed by pathology review at Brigham and Women's Hospital. Other confirmation of EBV-associated disease is acceptable, such as EBV DNA in situ hybridization, if EBER analysis is not adequate