A monoclonal antibody combined with a toxic substance that is used to treat certain types of acute myeloid leukemia in older patients and is being studied in the treatment of other types of cancer. Monoclonal antibodies are made in the laboratory and can locate and bind to substances in the body, including cancer cells. Gemtuzumab is a type of antibody-drug conjugate. Also called gemtuzumab ozogamicin and Mylotarg.