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. Lay abstract: Pembrolizumab (trade name Keytruda©) is a type of immune therapy that stimulates the body's immune system to fight cancer cells. This immune therapy can cause a variety of rashes. In this article, the authors describe a patient who developed a rash around hair follicles that is not commonly described with pembrolizumab. A man with a history of mildly infected hair follicles on his legs was diagnosed with advanced melanoma and was treated with pembrolizumab. After 19 treatments, he developed a rash on his legs, centered around hair follicles. Treatment with steroid ointments, steroid tablets and antibiotic tablets was not helpful. Pembrolizumab was stopped, but the rash persisted. A medicine called isotretinoin was required to control the rash. This type of rash has rarely been described with this kind of immune therapy, and isotretinoin might be required to treat it