Successful desensitization under antihistamine suppression in a case with urticaria due to osimertinib

Introduction Osimertinib is an approved therapy for patients with a Thr790met (T790M) mutation diagnosed with non-small cell lung cancer (NSCLC) that progresses during epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI) therapy. However, in 7-13% of patients, drug-related side effects lead to discontinuation of osimertinib treatment. In such cases, osimertinib desensitization is a treatment option that can be considered. Case report A 59-year-old female patient, who was followed up with the diagnosis of stage 4 NSCLC, was consulted to the allergy clinic because of urticaria. The patient developed urticaria plaques 20 h after the third dose of osimertinib tablet. Management & outcome With the diagnosis of osimertinib-induced urticaria, desensitization was planned for the patient. Treatment was started with a dose of 0.1 mg/day osimertinib. The procedure was completed in approximately 50 days, and a dose of 80 mg/day was reached with antihistamine suppression. Discussion Here, a successful osimertinib desensitization in a patient with a history of osimertinib-related type 1 allergic reaction is reported. Osimertinib desensitization is a treatment option that should be considered in cases where treatment has to be ceased due to drug-related side effects.