Osimertinib is an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) drug effective in patients with non-small cell lung cancer (NSCLC) harboring EGFR-TKI sensitivity and T790M resistance mutations. However, it is associated with hypersensitivity reactions like skin rash and urticaria. While slow desensitization protocols are documented in the literature, to our knowledge there are no reports of rapid desensitization with osimertinib.

We present successful rapid desensitization with osimertinib in a 64-year-old female with lung adenocarcinoma. She was diagnosed seven years ago and after six cycles of chemotherapy and six years on gefitinib, disease progression led to a repeat biopsy, revealing the EGFR 790M mutation. She started osimertinib at a dose of 80 mg, and on the fourth day of treatment, approximately 3-4 hours after drug administration, she developed urticaria on her arms and legs. Despite continuing treatment with methylprednisolone and an antihistamine, the urticarial rash persisted, leading to the discontinuation of osimertinib. Symptoms persisted for about a week before resolving. No alternative treatment options were available because the patient declined chemotherapy. A prick-to-prick test with osimertinib tablets was negative. To prevent treatment interruption, a six-step rapid desensitization protocol with osimertinib, adapted from crizotinib desensitization protocols, was used with bilastine premedication. No reaction occurred during desensitization. The patient continued osimertinib without any issues for six months.

Antineoplastic drug hypersensitivities are of paramount importance because alternative treatment options with equivalent efficacy are often unavailable. Desensitization to these drugs is crucial in the absence of alternative effective treatments and can be lifesaving.