Correlation of NPM1 immunohistochemistry with mutation subtypes, clinicopathologic variables and molecular testing in AML with NPM1 mutation.

BACKGROUND

Nucleophosmin 1 (NPM1) mutations define a major molecular subtype of acute myeloid leukemia (AML). Although RT-PCR and next-generation sequencing (NGS) remain the gold standard for diagnosis and minimal/measurable residual disease (MRD) assessment, NPM1 mutant-specific immunohistochemistry (NPM1m IHC) using monoclonal antibodies presents a rapid and cost-effective alternative. Correlation between NPM1m IHC patterns and specific NPM1 mutation subtypes remain underexplored.

OBJECTIVES

Evaluate the diagnostic utility of NPM1m IHC in AML with NPM1 mutation and to assess its correlation with mutation subtypes, morphologic features, cytogenetic profiles, co-mutations, and clinical outcomes.

METHODS

A retrospective cohort of 36 AML cases with confirmed NPM1 mutations (2018-2024) were analyzed for clinicopathologic variables, cytogenetics, PCR/NGS data, and NPM1m IHC results with subgroup analysis between Type A (n = 28) and non-Type A (n = 8) mutations.

RESULTS

NPM1m IHC positivity was observed in all insertional NPM1 mutation subtypes with two distinct staining patterns: homogeneous and two-toned, with two-toned pattern more frequent in Type A mutations. Non-Type A mutations were more often associated with complex karyotypes and showed a trend toward less frequent FLT3 co-mutations. Monocytic differentiation and cup-like nuclear morphology were assessed in both subgroups. No significant difference in survival or remission rates was observed between groups, although Type A mutations exhibited higher rates of dysplasia (p = 0.03).

CONCLUSION

NPM1m IHC is a sensitive and timely surrogate marker for insertional NPM1 mutations, correlating well with molecular results and useful in both immediate diagnosis and MRD evaluation. This study reveals subtype-specific morphologic and cytogenetic associations and highlights the need for further investigation into non-insertional NPM1 mutations and their detection challenges.