A Case of Stevens-Johnson Syndrome Induced by Selpercatinib.

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis are fatal adverse skin reactions characterized by high fever, epidermal detachment, and mucositis. Selpercatinib is a highly selective inhibitor of tyrosine kinase, rearranged during transfection (RET), and is the first targeted therapy for solid tumors with RET gene alteration. The main adverse events of selpercatinib include hypertension, liver dysfunction, diarrhea, and QT prolongation on electrocardiograms. We present the case of 50-year-old male with medullary thyroid carcinoma who was treated with selpercatinib. On the 12th day of the treatment, he developed widespread erythema, which resulted in a referral to our department. Physical examination revealed disseminated erythematous macules, conjunctival congestion, and bloody crusting of the lips, and histopathological examination showed single-cell necrosis in epidermis. Based on these findings, he was diagnosed with SJS. After the discontinuation of selpercatinib and systemic administration of corticosteroids, his symptoms were improved. The patient showed positivity for selpercatinib in drug lymphocyte stimulation test, suggesting the diagnosis of SJS induced by selpercatinib. To the best of our knowledge, this is the first report of SJS caused by selpercatinib. We herein present and discuss this case to raise awareness.