A drug that was used to treat acute myeloid leukemia (AML) that recurred (came back). It was used in older patients who were not able to take other anticancer drugs. Gemtuzumab ozogamicin was taken off the market but continues to be studied in clinical trials for the treatment of certain types of leukemia. It contains a monoclonal antibody that binds to a protein called CD33, which is found on some leukemia cells. It also contains a toxic substance, which may help kill cancer cells. Gemtuzumab ozogamicin is a type of antibody-drug conjugate. Also called Mylotarg.