A surrogate marker to detect nucleophosnim (NPM1) gene mutations in the cytoplasm of acute myeloid leukemia (AML) blast cells in 30 adult Iraqi patients

BACKGROUND AND OBJECTIVES: Acute myeloid leukemia (AML) with mutated nucleophosmin (NPM) gene has distinctive clinical and molecular features, and enormous advances have been achieved in the methods of diagnosing this new entity. This prospective study was designed to detect the mutant NPM protein using immunohistochemical staining in AML patients and to evaluate its application as a surrogate marker for NPM1 gene mutation analysis. DESIGN AND SETTINGS: This is a prospective study at a general community hospital in Baghdad (Baghdad Teaching Hospital) during the period from March 2011 to July 2011. PATIENTS AND METHODS: Immunohistochemical staining was used to detect the mutant NPM protein in bone marrow biopsies fixed in Bouin solution from 30 adult AML patients using anti-NPM polyclonal antibody. Molecular analysis was done on bone marrow or peripheral blood samples from 16/30 (53%) patients using single strand confirmatory polymorphism-reverse transcriptase-polymerase chain reaction (SSCP-RT-PCR). RESULTS: Using Immunohistochemical staining, 17/30 (56.7%) of AML patients were positive for the mutant NPM protein. The percentage of positive blast cells ranged from 30% to 100%. A significant relation was found between RT-PCR analysis and immunohistochemical staining (P=.009). The sensitivity of Immunohistochemical staining in detection of mutated NPM1 cases was 90%, whereas the specificity of this technique was 87.5%. CONCLUSION: The findings of immunohistochemical staining of NPM protein were significantly related with the molecular findings of NPM1 gene analysis, and the immunohistochemical staining technique was both sensitive and specific. These findings might be a prime step for the future utilization of this technique as a surrogate marker for the detection of NPM1 gene mutations in under-resourced countries as Iraq. Still, a larger study recruiting a larger number of patients will be useful for the assessment of the significance of immunohistochemical staining in the detection of minimal residual disease in NPM cytoplasmic positive AML, which is a good prognostic entity.