Dermatologic toxicities are the most common immune-related adverse events (irAE) secondary to immune checkpoint inhibitors (ICI). First-line treatment for grade 3 or 4 skin irAEs is high-dose corticosteroids, which have their own side effects. Prolonged treatment with corticosteroids may abrogate antitumor ICI activity. The cellular causes of these dermatologic toxicities, which can manifest as a variety of clinical presentations, remain unclear. Beyond steroids, recommended treatment options are limited. We report a case of psoriasiform dermatologic toxicity, induced by inhibition of PD-1 with the mAb pembrolizumab, which resolved after treatment with systemic interleukin IL17A blockade. Introduction of IL17A blockade did not alter the patient's melanoma response to pembrolizumab. This case suggests a possible pathogenic role of Th17 cells the irAE of the skin in this metastatic melanoma patient.
