Myelodysplastic syndromes without peripheral monocytosis but with evidence of marrow monocytosis share clinical and molecular characteristics with CMML.

MDS patients may present with monocytic marrow proliferation not fulfilling criteria for CMML. We analyzed MDS patients with or without a marrow monocytic proliferation by following up the amount of monocytic proliferation and characterizing their molecular profile. 315 MDS patients of Duesseldorf MDS registry were divided into two groups: A) 183 patients with monocytic esterase positive cells in marrow and monocytes between 101 and 900/μl in blood and B) 132 patients without monocytic esterase positive cells in marrow and monocytes in blood ≤100/μl. Twenty patients of each group were screened with regard to ASXL1, TET2, RUNX1, SETBP1, NRAS, and SRSF2 using Illumina myeloid panel. Group A patients were older, had significantly higher WBC, hemoglobin levels, neutrophils and platelets. CMML evolution rates were 4.9% and 1.5%, respectively (p=n.s.). TET2, NRAS and SRFS2 mutation frequencies were higher in group A and four patients had coexisting TET2 and SRFS2 mutation, which was shown to be characteristic but not specific for CMML. MDS patients with marrow monocytic proliferation have a more CMML-like pheno- and genotype and develop CMML more often. Those patients could potentially be very early stages of CMML or represent a CMML-like myeloid neoplasma with marrow adherence of the monocytic cell population.