First successful desensitization with Abemaciclib in an adult patient with breast cancer: A case report

Abemaciclib, a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, is an effective targeted therapy for hormone receptor-positive (HR+), HER2-negative, advanced or metastatic breast cancer. While nonimmediate hypersensitivity reactions (NIHRs) have been reported, no immediate hypersensitivity reactions (IHRs) to abemaciclib have been documented to date. Here, we report the first successful desensitization protocol for a patient who developed IHR to abemaciclib. A 75-year-old female with stage II breast cancer underwent a partial mastectomy followed by chemotherapy. Abemaciclib was initiated as part of adjuvant treatment. One hour after the third dose, she presented to the emergency department with lip swelling and urticaria. Symptoms resolved following the administration of intravenous methylprednisolone (0.5 mg/kg) and maleate pheniramine (45.5 mg/mL). Skin prick testing with abemaciclib was negative; however, a drug provocation test led to recurrence of urticaria at a cumulative dose of 150 mg. Given the clinical necessity of abemaciclib and the lack of alternatives, a 12-step desensitization protocol was implemented using 300 mg of abemaciclib dissolved in 100 mL of distilled water. The protocol was completed over 4 h, with no complications observed during the procedure or in the subsequent 3-month follow-up. The patient continued abemaciclib at 300 mg/day without recurrence of symptoms. This case highlights the importance of drug desensitization in oncology, particularly in patients for whom no alternative therapies are available.