Genetic Diversity Drives Differing Morphological and Clinical Presentation and Survival in Myelodysplastic-Type CMML with a Low Absolute Monocyte Count
Authors: Lachowiez Curtis A , Asimomitis Georgios , Bernard Elsa , Tazi Yanis , Creignou Maria , Germing Ulrich , Gattermann Norbert , Gilkes Amanda , Thomas Ian , Bullinger Lars , Döhner Konstanze , Malcovati Luca , Russell Nigel H. , Cazzola Mario , Döhner Hartmut , Huntly Brian J P , Hasserjian Robert P , Hellstrom Lindberg Eva , Loghavi Sanam , Papaemmanuil Elli 
Published: December 2024

Background:
The World Health Organization (WHO 5th ) and International Consensus Classification (ICC) revised the defining criteria of chronic myelomonocytic leukemia (CMML), lowering the absolute monocyte count (AMC) threshold for diagnosing CMML from 1 x109/ L to 0.5 x109/ L while retaining the requirement for a relative monocyte count of ≥10%. This study aimed to compare the phenotypic manifestations and genetic landscape of AMC of 0.5- &lt;1.0 x 109/L (AMClow) CMML to cases of CMML with AMC of ≥1 × 109/ L (AMChigh).
Methods
As all AMClow cases are (by definition) myelodysplastic-type CMML (MD-CMML; WBC &lt;13 × 109 /L) we restricted comparisons to AMChigh MD-CMML. Molecular and clinical data were queried from the International Working Group for Prognosis in MDS (IWG-PM) cohort of adult patients with myeloid neoplasms (N= 3,323).
Demographics were analyzed using descriptive statistics with between-group differences assessed using the Wilcoxon rank-sum test or Fisher's exact test. Leukemia free (LFS) and overall survival (OS) were analyzed using the log-rank method. Factor analysis of mixed data was employed for dimensionality reduction to assess the inter-relationship between categorical features (i.e., mutation present vs. absent) and quantitative variables (i.e., AMC, hemoglobin, etc.). Multivariable analysis (MVA) utilized Cox proportional hazards regression modeling.
Results
469 patients (pts) met WHO 5th and ICC criteria for MD-CMML, including 264 pts with AMClow and 205 pts with AMChigh. Notable clinical differences between AMClow vs. AMChigh cases included lower median BM blasts (3% vs. 3.4%, p: 0.007), median absolute neutrophil count (2.2 vs. 3 x109/L, p &lt; 0.001), hemoglobin (9.8 vs. 10.7 g/dL, p: 0.001), relative monocytes (14% vs. 25%, p &lt; 0.001) and a higher median platelet count (159 vs. 121 x109/L, p: 0.002).
Co-mutation analysis across discretized AMC categories (AMClow vs. AMChigh) revealed distinct associations between genotype and AMC. AMChigh cases were enriched for mutations (mut) in TET2 (60% vs. 46%, p: 0.005), SRSF2 (31% vs. 19%, p: 0.002), CBL (10% vs. 4%, p:0.008), KRAS (14% vs. 2%, p &lt; 0.001), NRAS (9% vs. 3%, p: 0.008), and PTPN11 (5% vs. 0.3%, p &lt; 0.001), while SF3B1 (34% vs. 15% p &lt; 0.001) and DNMT3A mut (19% vs. 9%, p: 0.005) were more frequent in AMClow cases. Biallelic TET2 mut (48% vs. 22%, p &lt; 0.001) and co-occurring mut in TET2 and SRSF2 (24% vs.11%, p &lt; 0.001) were also more frequent in AMChigh cases while del(5q) abnormalities were more common in AMClow cases (7% vs. 3%, p: 0.022)
When evaluating the overlap of presenting clinical and molecular features using factor analysis of mixed data, biallelic TET2 and TET2/SRSF2 mut (versus wild-type TET2 and SRSF2) were associated with higher AMC, while SF3B1 mut was associated with lower hemoglobin and higher platelet counts. RAS pathway mut (N/KRAS, CBL, NF1, and PTPN11) correlated with increased BM blasts, AMC, and monocyte percentage.
In accordance with the varied genetic landscape of AMClow vs. AMChigh, LFS was superior in AMClow vs. AMChigh MD-CMML (median 2.87 vs. 4.03 years, p: 0.037), with a trend towards longer OS (median 3.61 vs. 4.33 years, p: 0.055). However, genetic factors influenced survival more robustly, irrespective of the AMC group. In MVA, after adjusting for baseline hematologic parameters and differing molecular aberrations, RAS pathway mut were associated with an increased risk (HR: 1.60, 95% CI 1.13-2.26, p: 0.007) and SF3B1 mut was associated with a decreased risk of death (HR: 0.72, 95% CI: 0.50-1.05, p: 0.016) while AMClow vs. AMChigh did not retain significance (HR: 0.76, 95% CI: 0.52-1.09, p: 0.13).
Conclusions
In patients with MD-CMML, the clinical disease presentation and patient outcomes appear to be driven by underlying molecular abnormalities rather than AMC. Accordingly, with the recent reduction in the AMC count to 0.5 x109/ L for the classification of CMML, a portion of newly included CMML cases share overlapping genetics and blood count parameters with myelodysplastic neoplasms (MDS) . The molecular profile of a subset of AMClow cases overlapped with AMChigh cases, suggesting the AMClow group is genetically heterogeneous, with some cases more similar to AMChigh CMML and others more similar to MDS. This shared molecular ontogeny correlates with the clinical features of disease presentation, suggesting that molecular-based criteria may better define AMClow CMML and refine disease classification.