Cytomegalovirus and glioblastoma; controversies and opportunities

One of the more polarized ongoing debates in the brain tumor field over recent years has centered on the association of cytomegalovirus (CMV) with glioblastoma. Several laboratories have reported the presence of CMV antigens in glioblastoma patient specimens, whereas others have failed to detect them. CMV genomic DNA and mRNAs have been detected by PCR, but not in next-generation sequencing studies. CMV promotes high grade glioma progression in a mouse genetic model, and many CMV proteins promote cancer hallmarks in vitro, but actively replicating virus has not been isolated from tumor samples. A consensus is gradually emerging in which the presence of CMV antigens in glioblastoma is increasingly accepted. However, it remains challenging to understand this mechanistically due to the low levels of CMV nucleic acids and the absence of viral replication observed in tumors thus far. Nonetheless, these observations have inspired the development of novel therapeutic approaches based on anti-viral drugs and immunotherapy. The potential benefit of valganciclovir in glioblastoma has generated great interest, but efficacy remains to be established in a randomized trial. Also, early stage immunotherapy trials targeting CMV have shown promise. In the near future we will know more answers to these questions, and although areas of controversy may remain, and the mechanisms and roles of CMV in tumor growth are yet to be clearly defined, this widespread virus may have created important new therapeutic concepts and opportunities for the treatment of glioblastoma.