Busulfan-induced sideroblastic anemia

Patients in the stable phase of chronic myelogenous leukemia (CML) are usually treated with busulfan. The bone marrow of patients with CML may be exquisitely sensitive to busulfan, and occasionally such patients develop pancytopenia, secondary to hypoplasia or aplasia of the bone marrow, which is presumed to be due to busulfan-induced marrow toxicity. We report a case of Philadelphia chromosome-positive CML who developed pancytopenia while being treated with busulfan; however, the patient's bone marrow was not hypoplastic or aplastic but rather hyperplastic with sideroblastic changes. Busulfan is not known to cause sideroblastic changes, so this was considered to herald a transformation into acute leukemia. Busulfan was stopped, and only supportive treatment was given. To our surprise approximately 22 weeks after busulfan was stopped, the sideroblastic changes had disappeared and the bone marrow again showed features of CML. This case suggests that busulfan may cause sideroblastic anemia.