RATIONALE: Drugs used in chemotherapy work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Monoclonal antibodies, such as gemtuzumab, can block cancer growth in different ways. Some block the ability of cancer cells to grow and spread. Others find cancer cells and help kill them or carry cancer-killing substances to them. Sometimes the cancer may not need more treatment until it progresses. In this case, observation may be sufficient. It is not yet known whether combination chemotherapy is more effective than observation when given as maintenance therapy in treating acute promyelocytic leukemia.