Research on the potential of oncolytic viruses to treat various cancer types has waxed and waned over the past decade as promising early results failed to translate into clinical successes. However, these cancer destroying missiles are now firmly back on the industry's radar screen following the late 2015 FDA approval of the first oncolytic virus agent, Amgen Inc.'s Imlygic (talimogene laherparepvec) for nonresectable metastatic melanoma. The therapeutic is derived from a herpes simplex virus that has been genetically engineered to infect cancer cells and to generate granulocyte macrophage colony-stimulating factor (GM-CSF).