Day 22 of induction therapy is important for minimal residual disease assessment by flow cytometry in childhood acute lymphoblastic leukemia.

This study was aimed to illustrate the significance of minimal residual disease (MRD) assessment on day 22 in childhood acute lymphoblastic leukemia. MRD were measured on day 22, day 36, week 12, month 6 and month 12 by four-color flow cytometry. The 5-year cumulative incidence of relapse was significantly different for patients with MRD levels of <0.01%, 0.01-0.1%, 0.1-1.0% and ≥ 1.0% on day 22: 6.9 ± 2.6%, 16.7 ± 5.5%, 25.8 ± 6.2% and 58.4 ± 13.4% (P < 0.001). MRD on day 22 was more powerful than other parameters including NCI risk. However, other time points after induction, although predictive as well, were not accurate enough due to false positivity.