Peripheral blasts on day 21 of induction chemotherapy in a patient with core binding factor acute myeloid leukemia: more than meets the eye.

The combination of fludarabine, high-dose cytarabine, gemtuzumab ozogamicin, and granulocyte colony-stimulating factor (G-CSF), the FLAG-GO protocol, has resulted in excellent response rates and superior relapse-free survival as first-line therapy for patients with core binding factor acute myeloid leukemia (AML). A side effect of administration of G-CSF is an increase in peripheral white blood cell count and blast cell percentage during the recovery phase of the bone marrow after induction chemotherapy. A 60-year-old man with inversion 16 AML was admitted for induction chemotherapy with the FLAG-GO protocol at our institution. On day 21 of his induction regimen, he was noted to have blasts in both the peripheral smear and in the bone marrow that resolved on their own without any intervention by day 28. Our case report underscores the importance of recognizing this phenomenon associated with the administration of G-CSF, and waiting for 5-7 days before administering re-induction therapy or classifying the disease as primary refractory AML.