Fig. 1

a Massive infiltration of BM by NPM1-mutated AML cells showing the expected nuclear plus aberrant cytoplasmic positivity for nucleophosmin-1 (×400). b The same case as (a), showing a comparable number of leukemic cells expressing the IDH1-R132H mutant; positivity is mostly restricted to the cytoplasm of blast cells (×400). c Marked infiltration of BM by NPM1-mutated AML cells showing the expected nuclear plus aberrant cytoplasmic positivity for nucleophosmin-1. The rare elements with nucleus-restricted positivity for NPM1 represent residual normal hematopoietic cells (×400). d The same case as (c), showing that leukemic cells expressing the IDH1-R132H mutant represent only a small subclone of the total population of NPM1-mutated cells (×400). e Marked infiltration of BM by NPM1-mutated AML cells showing the expected nuclear plus aberrant cytoplasmic positivity for nucleophosmin-1 (×400). The arrow points to a positive megakaryocyte. Elements with nucleus-restricted positivity for NPM1 represent normal residual hematopoietic cells (×400). f The same case as (c), showing that the percentage of leukemic cells expressing the IDH1-R132H is slightly inferior to that of NPM1 cytoplasmic-positive cells. As in (e), the IDH1-R132H mutant is present both in mononuclear blast cells and in a megakaryocyte (arrow). The IDH1-R132H negative cells represent normal residual hematopoietic cells (×400). g Massive bone marrow infiltration by leukemic cells with nucleus-restricted positivity for nucleophosmin-1 (predictive of absence of NPM1 mutations, confirmed molecularly) (×400). h Specificity of the antibody against IDH1-R132H is demonstrated by the negativity of leukemic cells molecularly carrying the IDH1-R132C mutation (×400). (a–h) Dako REAL Detection System Alkaline Phosphatase/RED rabbit/mouse