CD33 and cancer: With a response rate of 26%, it was firstly approved by the FDA for use in patients with relapsed or refractory (r/r) CD33 positive AML in first relapse who were over 60 years and were not suitable for other conventional chemotherapies.145 Roughly 85–90% of adult and pediatric AML are CD33 positive.146 After binding with CD33 antigens and internalization by cancer cells, followed a hydrolysis of hydrazone bond to release calicheamicin.