OBJECTIVETo estimate the significance of the adjustment of acute lymphoblastic leukemia (ALL) risk group by monitoring minimal residual disease(MRD).

METHODTotally 285 children ALL patients who were diagnosed and systematically treated according to CCLG-2008 in Institute of Hematology and Blood Diseases Hospital, CAMS and PUMC, from April 2008 to August 2011 were prospectively selected. Among these cases, 62.8% (n = 179) were boys and 37.2% (n = 106) were girls and the median age was 5.3(0.5-14.0). The patients who were at high-risk group initially were excluded. The grouping of cases: the patients were divided into two groups according to the dates of initial diagnosis. Group I had 126 patients who were initially diagnosed between April 2008 and December 2009 in whom therapeutic regimen was not adjusted by reassignment of risk group by MRD. Group II had 159 patients who were initially diagnosed between January 2010 and August 2011 whose therapeutic regimen was adjusted by reassignment of risk group by MRD at specific time (33rd day of induction chemotherapy and 12 weeks after the beginning of chemotherapy). MP-FCM Coulter FC-500 was used in the detection of MRD.

RESULTAmong these 285 patients, 94.0% (n = 268) were diagnosed as B-lineage acute lymphoblastic leukemia and 6.0% (n = 17) were T-lineage acute lymphoblastic leukemia. In group I, 61.9% (n = 78) patients belonged to low-risk group, 38.1% (n = 48) median-risk; in group II, before the adjustment, the rates of the low-risk group and median-risk group were 68.6% (n = 109) and 31.4% (n = 50) , respectively, while after the adjustment they were altered to 53.5% (n = 85) and 39.6% (n = 63) , furthermore 6.9% (n = 11) patients went into the high-risk group. Both groups were followed up for 2.5 years after their diagnoses, the disease of 7.4% (n = 21) patients relapsed, and the rates of two groups were 12.7% (n = 16) and 3.1% (n = 5) respectively, P = 0.009. The rate of serious infection (such as sepsis, pulmonary infection) of all these patients was 32.3% (92/285) , there was no significant difference between the two groups [28.6% (36/126) vs.35.2% (56/159) , P = 0.392]. The mortality of all these patients was 6.7% (19/285) , and that of group I was higher than that of group II [10.3% (13/126) vs. 3.8% (6/159) , P = 0.044]. The 2.5 years overall survival (OS), event-free survival (EFS) and disease-free survival (DFS) of group I were all lower than those of group II in Kaplan-Meier survivorship analysis (all P < 0.05). The two groups were followed up for 2.5 years after their diagnoses, after elimination of the confounding influence of sex, age, FAB subtype, WBC count, ratio of blast cells in bone marrow at diagnosed, chromosome karyotype and fusion gene, reassignment of risk group by MRD was used to calculate the OS, EFS and DFS of ALL patients (all P < 0.05). After the adjustment the risk group was more significant in the assessment of prognosis.

CONCLUSIONThe reassignment of risk group in low and median risk groups children with acute lymphoblastic leukemia by MRD did not increase the rate of serious infection but could reduce the relapse rate and mortality, and was beneficial to increase the patients' OS, EFS and DFS.