Two instances of successful oral desensitisation following hypersensitivity reaction in a patient receiving osimertinib: a case report

Background Osimertinib is an irreversible epidermal growth factor receptor (EGFR) tyrosine‐kinase inhibitor (TKI) and an available therapy for patients with non‐small cell lung cancer (NSCLC) that have an EGFR or T790M mutation. It has become the preferred TKI in this patient group as it is superior to first‐generation TKIs; however, osimertinib may be discontinued due to various toxicities or reactions. Aim We report two instances of successful osimertinib desensitisation in a 70‐year‐old woman requiring treatment for NSCLC following two hypersensitivity reactions presenting as angioedema and urticaria. Clinical details Osimertinib desensitisation started at 5 mg/day and was gradually increased to 80 mg/day over a period of 30 days. Outcomes The patient continued osimertinib 80 mg daily for over a year until treatment was withheld for 4 weeks due to thrombocytopenia and diverticulitis. She restarted osimertinib, completing a second desensitisation to a reduced dose of 40 mg daily without serious adverse effect. The patient continues reduced‐dose osimertinib with stable disease. Conclusion This case report proposes an osimertinib desensitisation strategy useful for select patients experiencing osimertinib‐induced hypersensitivity reactions. It also demonstrates that if there is prolonged disruption to treatment, a second desensitisation can be completed successfully in the same patient so effective treatment in NSCLC may be continued.