Osimertinib-induced aplastic anemia after curative surgery for EGFR-mutant lung adenocarcinoma.

Osimertinib, a third-generation epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI), is widely used to treat EGFR-mutated non-small cell lung cancer (NSCLC) because of its high efficacy and favourable safety profile. However, rare but serious hematologic toxicities such as aplastic anemia may occur because of osimertinib use. Here, we report a case of severe aplastic anemia in a 75-year-old woman treated with osimertinib because of postoperative recurrence of EGFR-mutated lung adenocarcinoma. The patient had previously received adjuvant oral tegafur-uracil for 2 years without any hematologic toxicity. Lymph node recurrence was diagnosed 4.5 years after surgery, and osimertinib therapy was initiated. After approximately 19 weeks, the patient developed pancytopenia including grade 3 thrombocytopenia, which necessitated drug discontinuation. Bone marrow biopsy revealed a severely hypocellular marrow without dysplastic or malignant features, confirming the diagnosis of drug-induced aplastic anemia. Treatment with cyclosporine led to gradual hematologic improvement and transfusion independence. This is a rare case of osimertinib-induced aplastic anemia occurring after curative-intent surgery for NSCLC, in contrast to previously published reports that mainly involved patients with advanced or metastatic disease. Clinicians should be aware of this rare but life-threatening complication and closely monitor peripheral blood counts during treatment, particularly within the first 2-8 months after treatment initiation.