<div>Abstract<p>On September 1, 2017, the FDA granted approval for gemtuzumab ozogamicin (Mylotarg; Pfizer Inc.) in combination with daunorubicin and cytarabine and as a monotherapy for the treatment of adult patients with newly diagnosed CD33-positive acute myeloid leukemia (AML). Gemtuzumab ozogamicin is a CD33-targeted antibody–drug conjugate joined to calicheamicin. Approval of gemtuzumab ozogamicin combination treatment was based on a randomized trial of 271 patients with newly diagnosed AML treated with daunorubicin and cytarabine with or without 3 mg/m<sup>2</sup> fractionated gemtuzumab ozogamicin, which resulted in an event-free survival (EFS) of 13.6 months for gemtuzumab ozogamicin + daunorubicin and cytarabine and 8.8 months for daunorubicin and cytarabine alone [HR = 0.68 (95% confidence interval (CI), 0.51–0.91)]. Hemorrhage, prolonged thrombocytopenia, and veno-occlusive disease were serious toxicities that were more common in patients treated with gemtuzumab ozogamicin + daunorubicin and cytarabine. Approval of gemtuzumab ozogamicin monotherapy was based on a randomized trial of 237 patients with newly diagnosed AML treated without curative intent. Median overall survival (OS) was 4.9 months with gemtuzumab ozogamicin versus 3.6 months on best supportive care [HR = 0.69 (95% CI, 0.53–0.90)]. Adverse events were similar on both arms. Postapproval, several studies are required including evaluation of fractionated gemtuzumab ozogamicin pharmacokinetics, safety of combination gemtuzumab ozogamicin in the pediatric population, immunogenicity, and the effects of gemtuzumab ozogamicin on platelet function. <i>Clin Cancer Res; 24(14); 3242–6. ©2018 AACR</i>.</p></div>