Amgen's ($AMGN) Imlygic became the first genetically modified oncolytic viral therapy to earn FDA approval. It's indicated to treat recurrent melanoma following surgery. Imlygic is a modified herpes simplex type 1 virus that replicates within tumors and releases a protein called granulocyte-macrophage colony-stimulating factor. GM-CSF kills tumors, which results in the spread of tumor-derived antigens that may stimulate the immune system, along with GM-CSF itself. Interestingly enough, Amgen says the precise mechanism of action is unknown, a sure sign that the medicine lies at the frontiers of drug delivery. Release | More from FierceBiotech