Talimogene laherparepvec (TVEC) is a genetically modified, live oncolytic herpes simplex virus 1 therapy containing the granulocyte macrophage colony stimulating factor gene (GM-CSF). Approved by the US Food and Drug Administration in 2015 for treatment of unresectable melanoma in the skin and lymph nodes, this injectable immunotherapy delivers an antitumor effect through improved antigen presentation, T-cell priming, and by direct lysis of tumor cells.1 Response to therapy is generally assessed clinically through lesion regression. However, assessment may be confounded by pigment retention in the absence of persistent melanoma.