LAUSR

Talimogene laherparepvec (T‐VEC) is a novel intralesional oncolytic genetically modified herpes simplex virus type 1 vector for the treatment of unresectable cutaneous, subcutaneous, and nodal melanoma. Although immunological therapies such as T‐VEC offer therapeutic promise, they carry a risk of immune‐related adverse events (irAEs), the full spectrum of which is incompletely understood. We report a 63‐year‐old previously healthy man with cutaneous melanoma of the right ankle and progressive right lower extremity in‐transit metastases despite systemic therapy with immunomodulatory and molecularly targeted treatments. T‐VEC treatment resulted in a complete pathologic response on scouting biopsies. Biopsy of the right lateral calf showed lobular and septal panniculitis with lymphoplasmacytic infiltrate and lipophages. Gomori methenamine silver (GMS) stain and acid‐fast bacilli (AFB) stains were negative, and no polarizable foreign material was noted. T‐VEC was discontinued due to complete pathologic response and, in part, concern for development of irAEs including this panniculitis and an early concomitant autoimmune colitis. This case highlights a previously unreported irAE with this novel treatment for advanced cases of melanoma.