Track

Abstract

Immune checkpoint inhibitor (ICI)-induced psoriasis typically develops within 5–12 weeks of initiating therapy. We report a case of markedly delayed onset. A 67-year-old woman with lung adenocarcinoma in remission after 2 years of pembrolizumab (discontinued 24 months earlier) and locally advanced cutaneous squamous cell carcinoma treated with cemiplimab (discontinued 18 months earlier) presented with a pruritic, bumpy rash on both lower extremities. Punch biopsies from each leg revealed psoriasiform dermatitis with significant spongiosis and exudative scale crust. Periodic acid–Schiff and Gram stains were negative for microorganisms. Histologic findings suggested a “hybrid dermatitis,” with differential diagnosis including nummular eczema versus eczematized psoriasis. However, given her ICI history, a treatment-related etiology was also considered. This case highlights that cutaneous adverse effects from ICIs can manifest long after discontinuation. To our knowledge, this represents the most delayed onset of ICI-associated psoriasiform dermatitis reported in the literature, occurring 18–24 months after cessation of therapy.