CNL and aCML should be considered as single entity based on molecular profiles and outcomes.

Chronic neutrophilic leukemia (CNL) and atypical chronic myeloid leukemia (aCML) are rare myeloid disorders that are challenging with regard to diagnosis and clinical management. To study the similarities and differences of these disorders we undertook a multi-center international study of one of the largest case series (CNL, n=24; aCML, n=37 cases, respectively), focusing on the clinical and mutational profiles (n=53 with molecular data) of these diseases. We found no differences in clinical presentation or outcomes between both entities. As previously described, both CNL and aCML share a complex mutational profile with mutations in genes involved in epigenetic regulation, splicing and signaling pathways. Apart from CSF3R, only EZH2 and TET2 were differentially mutated between them. The molecular profiles support the notion of CNL and aCML being a continuum of the same disease that may fit best within the myelodysplastic/myeloproliferative neoplasms (MDS/MPN). We identified four high-risk mutated genes, specifically CEBPA (β=2.26, HR=9.54, p=0.003), EZH2 (β=1.12, HR=3.062, p=0.009), NRAS (β=1.29, HR=3.63, p=0.048) and U2AF1 (β=1.75, HR=5.74, p=0.013) by multivariate analysis. Our findings underscore the relevance of molecular-risk classification in CNL/aCML as well as the importance of CSF3R mutations in these diseases.