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

OBJECTIVES: To evaluate peripheral blood (PB) for minimal residual disease (MRD) assessment in adults with acute lymphoblastic leukaemia (ALL). METHODS: We analysed 76 matched bone marrow (BM) aspirate and PB specimens independently for the presence of ALL MRD by six-colour flow cytometry (FC). RESULTS: The 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. CONCLUSIONS: The 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.