Mycosis Fungoides Following <scp>IL</scp> ‐17 Inhibitor Treatment: A Case Series of Five Patients

IL-17 inhibitors are a class of biological agents used in the treatment of moderate-to-severe plaque psoriasis. We report five cases initially treated for psoriasis with IL-17 inhibitors that subsequently showed disease progression and were ultimately diagnosed with mycosis fungoides (MF), and provide a summarized analysis of their clinical features. We hypothesize that IL-17 inhibitors may promote the progression of MF by impairing anti-tumor immune responses and disrupting the Treg/Th17 balance. In psoriasis patients with atypical clinical manifestations or poor response to biologic therapy, the possibility of MF should be considered, and a skin biopsy is recommended prior to treatment when necessary to establish a definitive diagnosis.