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Immunohistochemical detection of cytoplasmic nucleophosmin in formalin-fixed paraffin-embedded marrow trephine biopsies in acute myeloid leukaemia
  1. Benny Man Wai Lit1,
  2. Yok Lam Kwong2,
  3. Kit Fai Wong1
  1. 1Department of Pathology, Queen Elizabeth Hospital, Hong Kong, China
  2. 2Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong, China
  1. Correspondence to Professor Yok Lam Kwong, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Pokfulam Road, Hong Kong, China; ylkwong{at}hku.hk

Abstract

Aims Nucleophosmin (NPM1) gene mutations resulting in cytoplasmic delocalisation of nucleophosmin (NPMc+) are the most common genetic abnormality in acute myeloid leukaemia (AML). In this study, we tested whether immunohistochemical (IHC) detection of cytoplasmic NPM1 (cNPM1) in formalin-fixed bone marrow trephine biopsies correlated with NPM1 mutations and the prognostic impact of NPM1 and fms-related tyrosine kinase 3-internal tandem duplication (FLT3-ITD) gene mutations was also assessed.

Methods A total of 71 Chinese adult de novo AML cases were evaluated for cNPM1 by IHC where the bone marrow trephines were fixed in 10% buffered formalin and decalcified by 5% EDTA. NPM1 and FLT3-ITD gene mutations were also investigated using PCR, fragment analysis and direct DNA sequencing.

Results IHC analysis of cNPM1 had a very good sensitivity (86.7%) and excellent specificity (96.4%) for NPM1 mutation. The positive predictive value was 86.7% and the negative predictive value was 96.4%. NPM1 mutations and FLT3-ITD were closely associated (p=0.003). Patients with mutated NPM1 and without FLT3-ITD mutation have a longer overall survival (p=0.042) than patients with both NPM1 and FLT3-ITD mutations.

Conclusions Our results showed that IHC detection of cNPM1 in formalin-fixed trephine biopsies correlated well but not entirely with NPM1 mutation. Furthermore, NPM1 mutations were significantly more frequent in FLT3-ITD than FLT3-wild-type cases.

  • LEUKAEMIA
  • IMMUNOHISTOCHEMISTRY
  • CYTOGENETICS

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