Flow cytometric minimal residual disease assessment of peripheral blood in acute lymphoblastic leukaemia patients has potential for early detection of relapsed extramedullary disease

ObjectivesTo evaluate peripheral blood (PB) for minimal residual disease (MRD) assessment in adults with acute lymphoblastic leukaemia (ALL).MethodsWe analysed 76 matched bone marrow (BM) aspirate and PB specimens independently for the presence of ALL MRD by six-colour flow cytometry (FC).ResultsThe overall rate of BM MRD-positivity was 24% (18/76) and PB was also MRD-positive in 22% (4/18) of BM-positive cases. We identified two cases with evidence of leukaemic cells in PB at the time of the extramedullary relapse that were interpreted as MRD-negative in BM.ConclusionsThe use of PB MRD as a non-invasive method for monitoring of systemic relapse may have added clinical and diagnostic value in patients with high risk of extramedullary disease.