Aplastic anaemia with small paroxysmal nocturnal haemoglobinuria clones developing during osimertinib therapy for non-small cell lung cancer.

We report two cases of aplastic anaemia (AA) with small populations of paroxysmal nocturnal haemoglobinuria (PNH)-phenotype cells that developed during osimertinib (OSIM) therapy for epidermal growth factor receptor mutation-positive lung adenocarcinoma (EGFR-LUAD). The first case was a 76-year-old woman with EGFR-LUAD accompanied by pleural dissemination. She developed pancytopenia 9 months after starting OSIM therapy. We diagnosed the patient with moderately severe AA and observed hematopoietic recovery following treatment with anabolic steroids and eltrombopag. The second case involved a 63-year-old woman diagnosed with EGFR-LUAD who received adjuvant chemotherapy with OSIM. She developed pancytopenia 6 months later and was diagnosed with non-severe AA. Cyclosporine and romiplostim treatment were effective, allowing for outpatient management. In the two cases described herein, a small number of PNH-phenotype cells were confirmed. The clinical importance of the small PNH-phenotype populations and the mechanism underlying AA during OSIM therapy remain unclear and warrant further investigation.