Pembrolizumab-induced follicular eruption and response to isotretinoin

Background: Pembrolizumab is a monoclonal antibody targeting PD-1. Folliculitis secondary to pembrolizumab has rarely been reported in the treatment of malignant melanoma. Case: A 49-year-old with a history of mild lower limb folliculitis developed metastatic malignant melanoma, and immunotherapy with pembrolizumab was initiated. Following 19 doses of pembrolizumab, a folliculocentric pustular eruption developed on the lower legs. Biopsy was consistent with folliculitis. Treatment with topical corticosteroids, high-dose prednisolone, lymecycline, clarithromycin, trimethoprim and clindamycin was unsuccessful. Pembrolizumab was stopped after 22 cycles, but the folliculitis persisted. Oral isotretinoin was required for disease control. Discussion: Drug-induced follicular eruptions have rarely been described with anti PD-1 therapy. Isotretinoin may be required to achieve remission.