Gemtuzumab ozogamicin given in combination with daunorubicin and cytarabine, has been shown to prolong the life span of patients for up to 8 months before the cancer has returned to manifest. This is the motivation that led the European Commission to authorize the marketing of the drug for the treatment of acute myeloid leukemia (AML). This is the European opinion although some side effects of gemtuzumab ozogamicin may be serious. Gemtuzumab ozogamicin is authorized for patients over the age of 15 without prior treatment for AML. The drug is used in patients whose tumor cells have CD33 protein on the surface (as is the case for most patients with acute myeloid leukemia). It is not used instead for acute promyelocytic leukemia (APL). AML is “rare” and gemtuzumab ozogamicin has been defined as an “orphan medicinal product” on 18 October 2000. Gemtuzumab ozogamicin should be administered by intravenous infusion over 2 hours. The patient usually receives 3 infusions over a week along with daunorubicin and cytarabine. If the tumor responds to the initial treatment, the patient may receive an additional “consolidation” treatment to prevent the tumor from recurring. The active substance consists of two parts: a cytotoxic substance and a monoclonal antibody. As the antibody binds to CD33 on leukemic cells, the cells absorb the antibody and the cytotoxic substance attached to it. Once inside the cells, calicheamicin is released exerting its cytotoxic effect. A main study involving 271 patients with acute myeloid leukemia (AML) has shown that the addition of gemtuzumab ozogamicin to daunorubicin and to citarabine can prolong the life span of patients by approximately 8 months without the tumor returning. For patients who received gemtuzumab ozogamicin in combination with daunorubicin and cytarabine, an average of 17.3 months passed before treatment failed, before the tumor returned or before the patient died, compared to 9.5 months for patients who received a combination of only daunorubicin and cytarabine. The most common side effects with Mylotarg given in combination with daunorubicin and cytarabine are bleeding and serious infections.