Follicular psoriasis induced by pembrolizumab in a patient with advanced non-small-cell lung cancer

A 69-year-old man with a history of hypertension, in therapy with doxazosin for nearly 10 years, was diagnosed with metastatic non-small-cell lung cancer (NSCLC). One year prior he had started immunotherapy with pembrolizumab, an anti-PD1 monoclonal antibody, at a dose of 200 mg once every three weeks. After the 4th infusion of pembrolizumab, the patient developed a moderate-to-severe skin rash. Based on the clinical appearance, medical history and dermatoscopic findings, a diagnosis of recurrence of psoriasis was made. Topical steroids and emollients were prescribed once a day on the affected body areas. Ten days later, at our dermatological evaluation, the psoriatic lesions and joint pain had improved. Pembrolizumab was never stopped.To the best of our knowledge, 34 cases of exacerbation or new onset of psoriasis during treatment with anti-PDL-1 or PD-1 therapy have been reported in the literature. Typical psoriatic plaques are the most frequent lesions reported.Follicular psoriasis (FP) is a rare entity that must be differentiated from other clinically similar diseases, especially keratosis pilaris.