Clinico-Haematologic association and prognostic relevance of NPM1 and FLT3-ITD mutations in acute Myeloid Leukaemia

Abstract

Background & objectives: Molecular genetic abnormalities have a significant role not only in diagnosis but also in determining the clinical course and prognosis. Nucleophosmin-1 (NPM-1) is associated with good prognosis while internal tandem duplication of the fms-like tyrosine kinase-3 gene (FLT3-ITD) confers a poor prognosis. Knowledge of the status of these mutations in AML patients not only guides treatment decisions but also helps in predicting response to frontline induction and consolidation chemotherapy as well as the risk of relapse and overall survival. Our objectives were to determine the prevalence, clinico-haematological features and immunophenotypic characteristics of AML patients with FLT3-ITD and NPM1 mutation and to evaluate the response to induction therapy (CR) and disease free survival (DFS) in this cohort of patients.

Methods: Patients diagnosed as AML from March 2015 to March 2017 at Armed Forces Institute of Pathology Rawalpindi were included in the study. Clinico-haematologic and immunophenotypic parameters were noted and molecular analysis for FLT3-ITD and NPM1 mutation was performed. Any correlation with cytogenetics or other molecular markers was also studied. Response to standard induction chemotherapy and disease-free survival were assessed.

Results: A total of 108 cases of AML were analyzed. Median age was 35 years and 64.8% were males. The median age of the study group was 35 years. Of these, 70 (64.8%) were males while 38 (35.2%) were females. Twenty-nine (26.9%) patients were NPM1 positive, twelve (11.1%) were FLT3-ITD positive while eight (7.4%) were positive for both mutations. Patients with NPM1 mutations were associated with female gender, higher haemoglobin level and platelet counts while those with FLT3-ITD mutations were predominantly seen in male patients and had significantly higher WBC counts, bone marrow blasts, biopsy cellularity and LDH levels. CR rates of NPM1 positive, FLT3-ITD positive and both mutation positive groups were 72%, 60% and 71%, respectively. The median disease-free survival was significantly lower in the FLT3-ITD positive group (7.1 months) as compared to the NPM1 positive group (16.1 months). The median disease-free survival was 12 months and 11.9 months in the NPM1 positive/FLT3-ITD positive and the NPM1 negative/FLT3-ITD negative groups, respectively.

Conclusion: AML patients harbouring NPM1 and FLT3-ITD mutations have distinct clinical and haematological characteristics. NPM1 mutations have a better CR and DFS as compared to FLT3-ITD group.

Keywords: Acute myeloid leukaemia; Complete response (CR); Disease free survival (DFS); FLT-3 ITD; NPM-1.

Fig.1

Complete response of the different subgroups.

Fig.2

CR duration of the patients.