Clinical and prognostic significance of eosinophilia and inv(16)/t(16;16) in pediatric acute myelomonocytic leukemia (AML-M4)

Background: The cytogenetic aberrations inv(16)(p13.1q22)/t(16;16)(p13.1;q22), frequently detected in acute myelomonocytic leukemia with eosinophilia (FAB type M4eo), are generally considered a prognostically favorable subgroup. M4eo comprises a distinct morphology compared to M4 without eosinophilia (M4eo-) and therefore may be indicative for a different pathogenesis. Procedures: Morphology and cytogenetic/molecular analyses of a Dutch cohort of pediatric acute myelomonocytic leukemia (AML-M4) patients were performed and studied in order to analyze the association between the presence of eosinophilia morphology (M4eo+), inv(16)/t(16;16) (inv(16)+), clinical features, and outcome. Results: Of the 119 included patients with available combined morphological and cytogenetic results, 60% had M4eo- without inv(16) (inv(16)-), 10% had M4eo-/inv(16)+, 13% had M4eo+/inv(16)-, and 17% had M4eo+/inv(16)+. M4eo+ was significantly associated with the presence of inv(16)/t(16;16) (P < 0.001). Patients with M4eo+ had no significantly superior outcome compared with patients with M4eo-, whereas patients with inv(16)+ had significantly superior probabilities of event-free survival and probabilities of overall survival compared with patients without inv(16)-. Patients with M4eo+/inv(16)+ had no significantly better outcome than those with M4eo-/inv(16)+. Conclusion: The prognostically favorable impact of distinct morphology with eosinophilia probably relies on its association with inv(16)/t(16;16). Simultaneous presence of both eosinophilia and inv(16) was not associated with superior outcome in our study. These results may be relevant for risk-group classification and risk-group adapted treatment and underline the importance of accurate cytogenetic analysis.