Bone Marrow Aplasia Under Tyrosine Kinase Inhibitors in Chronic Myeloid Leukemia: A Rare and Unpredictable Complication

Tyrosine kinase inhibitor (TKI)-induced bone marrow aplasia is a rare but potentially severe complication of chronic myeloid leukemia (CML). We report two cases occurring under imatinib and nilotinib in patients with chronic-phase CML. The first case, occurring six months after imatinib initiation, was characterized by severe bone marrow aplasia associated with gelatinous marrow transformation, a rare histological finding in TKI-treated CML. The second case, occurring two months after switching to nilotinib, evolved toward non-severe bone marrow aplasia, with complete hematologic recovery after treatment discontinuation. These observations illustrate the heterogeneity and unpredictability of this toxicity, which may occur across different TKI generations and levels of molecular response. Immediate TKI discontinuation remains essential, and any persistent pancytopenia should prompt early bone marrow evaluation to ensure a timely diagnosis and appropriate management.