NPM-1, but Not FLT3-ITD Mutations Predict Early Blast Cell Clearance and CR Rate in Patients with Normal Karyotype AML or High-Risk Myelodysplastic Syndrome (MDS).

Background: Mutations in the NPM1 gene represent the most frequent alterations in patients with AML and are associated with a favourable clinical outcome.

Patients and Methods: We analyzed 803 patients that were treated in the AMLCG2000 study. Patients with de novo or secondary AML or high-risk myelodysplastic syndrome (MDS) were randomly assigned upfront for induction therapy containing one course with standard dose and one course with high-dose cytarabine, or two courses with high-dose cytarabine, and in the same step received postremission prolonged maintenance or busulfan/cyclophosphamide chemotherapy with autologous stem-cell transplantation. At diagnosis mutations in the NPM1 and FLT3 gene were analyzed by routine molecular techniques.

Results: The median age of all patients was 60 years and the median observation time 23 months. Results of the mutations status of FLT3 (FLT3-ITD) and NPM1 were available in 761/803 (94,8 %) and 690/803 (85,9 %) patients, respectively. NPM1 and FLT3-ITD mutation were found in 352 (51,1%) and 199 (28,9%), respectively. On the basis of these two molecular markers, patients were grouped in 4 subgroups: 1. NPM1+/FLT3−, N=214 (31%), 2. NPM1+/FLT3+, N=138 (20%); 3. NPM1−/FLT3−, N=276 (40%); NPM1−/FLT3+ (9%).

The CR-rates were significantly higher in NPM1+ (74,4%) than in NPM1− (55,9%) patients, but were unaffected by the FLT3-ITD status. Overall survival (OS), event-free survival (EFS) and relapse free survival (RFS) was significantly higher in NPM1 positive and FLT3-ITD negative patients. In a multivariate analysis age, WBC, the presence of the NPM1 mutation and de novo AML were independent prognostic factors for the CR-rate. The NPM1− and FLT3 mutation status, age and LDH were identified as independent prognostic factors for RFS.

To further characterize the biological effects of NPM1 and FLT3 mutations, we analyzed the in vivo blast cell clearance measured by the residual bone marrow blast cells one week after the end of the first induction cycle (d+16 blasts). The percentage of patients with adequate blast cell reduction (residual bone marrow blast <10%) was significantly higher in NPM1+ patients (87,3%) compared to NPM1− (65,7%) patients. The presence of a FLT3-ITD mutation had no effect on early blast cell clearance.

Conclusions: The presence of a NPM1 mutation represents an independent positive prognostic factor for the CR-rate and RFS/OS. In contrast, FLT3-ITD mutations do not affect the CR-rate, but have a negative prognostic impact on RFS and OS. The higher sensitivity of NPM1-positive blasts towards the induction therapy point to a central role of NPM1 in the regulation of apoptotic cell death in AML.