Prospective Study on the Clinical Relevance of Residual Disease in Patients with Acute Myeloid Leukemia in Complete Remission

The initial goal of chemotherapy in patients with newly diagnosed acute myeloid leukemia (AML) is the achievement of a complete remission (CR). This can be reached in 60–80% of adult patients. Most CR patients will receive some form of postremission therapy to reduce the risk of relapse [1-6]. CR in AML is defined by less than 5% blast cells on light microscopic evaluation of bone marrow smears and by the regeneration of normal hematopoiesis. Since this method fails to detect residual cells in the majority of AML patients who will eventually relapse, efforts aim at the development of methods with higher sensitivity. Such molecular biological and immunological methods are based on the detection of leukemia-specific and/or leukemiaassociated cell markers. Specificity and sensitivity of these markers can be determined in laboratory experiments using bone marrow aspirates of patients with acute leukemia. The ultimate test for the relevance of these methods is the correlation of residual disease and hematological relapse. In the past three years we have concentrated on the application of multiparameter immunophenotyping using flow cytometry for the distinction of AML blasts from normal hematopoietic progenitors. The criterium was the aberrant expression of cell surface antigens [7–11]. In the initial analysis on bone marrow aspirates from 81 patients with newly diagnosed AML, the leukemic cells of 80 patients were distinguishable based on at least one aberrancy. The present, prospective study used the informations of the aberrant immunophenotype from the aspirate at diagnosis for detection of residual leukemic cells at achievement of hematological complete remission. Patients were followed for a minimum of 12 months or upto relapse. The CR duration was compared between patients with and without persistent cells carrying the leukemic immunophenotype.