Imlygic is a prescription drug used to treat melanoma lesions on the skin and in the lymph nodes. Melanoma is the most dangerous skin cancer. Imlygic belongs to a group of drugs called oncolytic viruses, which work by replicating inside cancer cells, causing the cells to burst and die. This medication is directly injected into melanoma lesions. Common side effects include fatigue, chills, nausea, flu-like symptoms, injection site pain and fever. Imlygic is a first-of-its-kind treatment for melanoma.