SOHO 2026 Annual Meeting

INTRODUCTION

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic / myeloproliferative neoplasm characterized by peripheral monocytosis and risk of acute leukemic transformation.

Myelofibrosis (MF), a myeloproliferative neoplasm (MPN), may exhibit monocytosis (MF-M), associated with increased progression risk.

Considerable diagnostic overlap exists between these two entities, but direct comparisons between their characteristics and outcomes is lacking.

AIM

To compare disease characteristics and outcomes between MF, MF-M, and CMML.

METHODS

This single-center study included patients meeting 2022 WHO monocytosis criteria: absolute monocyte count ≥0.5 x109/L, ≥10% of white blood cells (WBC), persistent >3 months.

Baseline characteristics and outcomes were compared using Wilcoxon rank sum, Pearson’s Chi-Squared, and Fisher’s exact test. Overall survival (OS) was estimated by Kaplan-Meier analysis.

CONCLUSIONS

•Median baseline WBC was greater in MF-M compared to MF but did not differ significantly from CMML. Median peripheral blast percentage was higher in MF-M than MF, but equivalent to CMML.

•Marrow fibrosis grade was similar between MF-M and MF, though higher in MF-M than CMML.

•MF-M had more frequent CMML-associated mutations than MF: SRSF2, RUNX1, NRAS. JAK2 mutations were less frequent in MF-M than MF.

•Transfusion dependence and splenomegaly did not differ between groups.

•From diagnosis, median OS was shorter in CMML than MF-M. From monocytosis onset, this difference was less pronounced. Adjusting for age, BM blasts, and adverse cytogenetics, CMML demonstrated worse OS than MF-M from diagnosis, but not monocytosis onset.•MF-M exists on a clinical and prognostic spectrum between MF and CMML.

•Despite possessing MF features (high-grade fibrosis and MPN-specific mutations), MF-M displays a higher burden of CMML-associated mutations with survival approaching CMML, suggesting CMML-directed therapies may be reasonably extended to this population.

SOHO 2026 Annual Meeting

Myelofibrosis With Monocytosis Is Clinically and Prognostically Similar to CMML

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