Minimal residual disease testing in acute leukemia by flow cytometry immunophenotyping: prognostic significance

Two main techniques are being used for the detection of minimal residual disease (MRD) in acute leukemia (AL): immunophenotypic analysis and polymerase chain reaction (PCR). In this paper, we analyze the results of assessing MRD by means of flow cytometry (FC) in a group of 93 patients with AL who were prospectively studied and treated in a single institution over a 9-year period. The presence or absence of MRD was established at a cut-off level of 2%, as judged by FC; a single result above this level was considered to define the positivity. The patients were grouped in 4 subsets: (1) acute lymphoblastic leukemia (ALL) patients with MRD (n = 36); (2) acute myeloblastic leukemia (AML) patients with MRD (n = 13); (3) ALL patients without MRD (n = 31); and (4) AML patients without MRD (n = 13). The relapse rates in these groups were 17%, 8%, 0%, and 0%, respectively, whereas the overall 7-year survival was 65%, 69%, 83%, and 98%, respectively. Our results support the usefulness of serially assessing MRD in patients with AL by means of FC; because this method is applicable to all cases of AL, despite being less sensitive than a molecular biology study; it is a good option to follow-up patients and to decide therapeutic and timely interventions.