It’s no new news that viruses cause cancer. For example, human papillomavirus (HPV) causes almost all of the more than 500,000 annual worldwide cases of cervical cancer. This makes sense: By driving the proliferation of infected cells, viruses speed manufacture of more viruses, but excessive cellular proliferation is also a hallmark of cancer. Now a University of Colorado Cancer Center review published in the journal Viruses explores another strategy that viruses use to ensure their own survival, also with the unfortunate byproduct of promoting cancer, namely the viral ability to manipulate the human immune system. This new understanding may help to increase the effectiveness of immune-based therapies against cancer.