Introduction

About 80 to 90% of children with newly diagnosed acute myeloid leukemia (AML) achieve complete remission (CR) with intensive induction chemotherapy. However, 10 to 20% of patients do not achieve remission, with early death from hemorrhage, leukostasis, infection, or resistant disease (primary refractory AML), and even after achieving remission, 30 to 40% of patients will relapse. Primary refractory AML and relapsed AML have a poor prognosis, with an overall survival of 25–35%. For patients in first relapse, the prognosis mainly depends on the time of relapse. If it is early, defined as within 1 year after initial diagnosis, the second CR rate is approximately 50% and overall survival 10–15%. If the time of relapse is late, defined as more than 1 year after diagnosis, the second CR rate is approximately 75% with an overall survival of up to 37%. Multiple-relapsed AML has an even worse prognosis. The management of refractory or relapsed AML is quite difficult. Several treatment schedules have been studied recently, and progress seems feasible with the use of new drugs and novel drug combinations followed by hematopoietic stem cell transplantation (HSCT).

Definition of relapse

Relapse is defined as the reappearance of leukemic cells at any site in the body. Most relapses in AML occur during treatment, mostly during the first year after diagnosis. Relapses after 2 years are rarely seen. Only exceptionally are relapses observed after more than 10 years, and in these patients it is uncertain whether the leukemic cells are the same clone found at diagnosis (relapse) or if they arose from a secondary (therapy-induced) leukemogenic event. This question is often difficult to resolve because of the lack of precise molecular and immunophenotypic techniques at the time the leukemia was first diagnosed.