haematologica/the hematology journal | 2006; 91(8) | 1109 |

Methodological approach to minimal residual disease detection by flow cytometry in adult B-lineage acute lymphoblastic leukemia Anumber of patients with adult acutelymphoblastic leukemia (ALL) whoachieve hematologic complete remis-sion subsequently have a relapse. Early assess-ment of treatment response is useful to design risk-adapted treatments.1-4 In childhood ALL, the presence of minimal residual disease (MRD) during treatment is associated with a significantly higher relapse risk, and is current-ly used to tailor treatment intensity.3-4 Flow cytometry is widely used for the diag-nosis of leukemia and is suitable for routine MRD assays.3,5-8 In childhood ALL results of flow cytometry and polymerase chain reaction (PCR) analysis can be highly concordant.9 MRD detection by flow cytometry is based on the identification of leukemia-associated immunophenotypes (LAIP), which are not expressed by normal bone marrow (BM) or peripheral blood cells.3-17 While T-ALL blasts normally express nuclear TdT/cytoplasmic CD3, a thymus-restricted marker combina-tion, in more than 90 % of cases, B-lineage ALL blasts usually share most phenotypes of nor-mal BM B-cell precursors. Thus, the identifica-tion of LAIP requires first that the phenotypic profiles of normal cells are fully character-ized.7-8,10-17 LAIP can be currently identified in 95 % of childhood ALL cases.7-8, 10-16 Fewer stud-ies have addressed the feasibility, sensitivity, reproducibility, and prognostic significance of flow cytometric MRD detection in adult ALL.7,11,17-18 We characterized adult normal BM B-cell precursors and compared the marker combinations to those expressed by adult B-lineage ALL blasts. We then assessed the expression stability of the identified pheno-types, and the potential prognostic significance of MRD monitoring using these phenotypes