Oncology's Trojan Horse: Using Viruses to Battle Cancer.

In 2016, the American health care system was faced with more than 1.6 million new cases of cancer, and individuals older than 65 years of age will be affected disproportionately. Many older individuals are poor candidates for traditional treatments (e.g., chemotherapy, radiation) because of actual or potential treatment-related adverse events. Researchers continuously look for novel therapeutic strategies, and an exciting new one is on the horizon: virotherapy. Viruses' ability to infect and kill human cells makes them promising cancer treatments. The greatest success has been seen in acute lymphocytic leukemia. To date, four genetically engineered oncolytic viruses have been approved globally by several countries' health regulatory agencies, but several challenges remain. Only one, talimogene laherparepvec (T-Vec), is available in the United States. Treatment-naive patients tend to respond better than patients receiving T-Vec as second-line therapy. Other good candidates for T-Vec include elderly patients who do not tolerate checkpoint inhibitors (the leading immunotherapy in advanced melanoma). Researchers continue to look for ways to increase oncolytic viruses' clinical potency. Once they do, these agents will become effective cancer therapy.

ABBREVIATIONS: GM-CSF = Genetically modified colony-stimulating factor, HIV = Human immunodeficiency virus, HSV-1 = Herpes simplex virus, OV = Oncolytic virus.