Clonal cytopenia of undetermined significance (CCUS) with dysplasia is enriched for MDS-type molecular findings compared to CCUS without dysplasia.

Objectives: Although morphologic dysplasia is not typically considered a feature of CCUS, we have consistently observed low-level bone marrow (BM) dysplasia among CCUS patients. We sought to determine whether sub-diagnostic BM dysplasia in CCUS patients is associated with other clinico-pathologic findings of myelodysplastic syndrome (MDS).

Methods: We identified 49 CCUS patients, 25 with sub-diagnostic dysplasia (CCUS-D), and 24 having no dysplasia (CCUS-ND). We compared the clinical, histologic, and laboratory findings of CCUS-D and CCUS-ND patients to 49 MDS patients, including blood cell counts, BM morphology, flow cytometry, cytogenetics, and results of next-generation sequencing.

Results: No statistically significant differences were observed between CCUS-D and CCUS-ND patients in the degree of cytopenias, BM cellularity, myeloid-to-erythroid ratio, or the presence of flow cytometric abnormalities. However, compared to CCUS-ND, CCUS-D patients exhibited increased mutations in myeloid malignancy-associated genes, including non-TET2/DNMT3A/ASXL1 variants, spliceosome (SF3B1, SRSF2, ZRSR2, or U2AF1) variants, and IDH2/RUNX1/CBL variants. CCUS-D patients were also enriched for higher variant allele frequencies and co-mutation of TET2/DNMT3A/ASXL1 with other genes.

Conclusions: CCUS-D patients exhibit a molecular (but not clinical) profile more similar to MDS patients than CCUS-ND, suggesting CCUS-D may represent a more immediate precursor to MDS and may warrant closer clinical follow-up.