Background: Clonal cytopenias of Undetermined Significance (CCUS) have a higher risk of progression to myeloid neoplasm (MN) compared to idiopathic cytopenias of undetermined significance (ICUS) (Malcovati et al., Blood, 2017). The implementation of flow cytometric (FC) immune-phenotyping and next generation sequencing (NGS) in clinical practice has improved the diagnosis of these entities but the clinical significance and interaction of these abnormal results are still unknown. In this study we investigated predictive factors that play role in survival and progression to MN in patients with ICUS/CCUS.

Methods: Patients (Pts) who had undergone evaluation for unexplained cytopenia and had undergone FC and bone marrow morphological assessment between 3/2015-3/2020 at Mayo Clinic Rochester were included. Pts were excluded if a malignant hematological disorder was diagnosed prior to the time of FC. FC included evaluation of the following parameters: Abnormal expression of HLA-DR/CD13, CD2, CD7, CD45, and CD56 on blasts; and abnormal CD13/CD16 expression and side scatter on granulocytic cells. NGS panel up to 2018 included 34 genes, ASXL1, BCOR, BRAF, CALR, CBL, CEBPA, CSF3R, DNMT3A, ETV6, EZH2, FLT3, GATA1, GATA2, IDH1, IDH2, JAK2, KIT, KRAS, MPL, MYD88, NOTCH1, NPM1, NRAS, PHF6, PTPN11, RUNX1, SETBP1, SF3B1, TERT, TET2, TP53, U2AF1, WT1, and ZRSR2; in 2018, BRAF was omitted and 12 genes were added, ANRD26, DDX41, ELANE, ETNK1, KDM6A, MYD88, NOTCH1, RAD21, SH2B3, SRP72, SMC3, and STAG2.

Results:

  1. Characteristics: Of 490 consecutive pts, 238 (median age 69 years (range 19-92), 66% males) met our inclusion criteria as ICUS. 86 (36%) pts had CCUS (abnormal cytogenetics and/or tested positive for pathogenic mutations on NGS). After a median follow-up of 28 months (95% CI: 20 to 31 months), 21 (25%) patients developed MN and 23 (27%) died during follow-up.

  1. Comparing ICUS vs CCUS: upon comparing CCUS pts to ICUS, several factors were found to be significantly different: CCUS pts were older (p= .02); majority male (p= .04), had more abnormal HLA-DR/CD13 (p <.0001), more side-scattered light by FC (p <.0001), more pancytopenia on follow up (p= .02) and more morphologic atypia (<.0001).

  1. Overall survival (OS) outcomes in CCUS: Several covariates were significant in univariate models, and model selection was used to generate a risk score based on abnormal CD7, abnormal CD13/CD16, abnormal HLA-DR/CD13, splenomegaly and history of prior chemotherapy or radiotherapy (range: 0 - 4; HR=2.58, [95 CI: 1.69 - 3.94], p<.0001). Risk scores were grouped as low risk (score=0), intermediate risk (score=1), and high risk (score=2+), with estimated 2-yr-OS of 95%, 84%, 40%, respectively (Figure 1). An extended risk score model including NGS factors added ASXL1 and IDH1 mutation status to the previous model (range: 0 - 6; HR=2.72, [95 CI 1.82 - 4.06], p<0.0001).

  1. MN-free survival (MNFS) in CCUS: 37 pts either progressed to MN and/or died with a median follow up time for MNFS of 22.4 months. Similar for OS, model selection approaches yielded a composite risk score: splenomegaly, BCOR mutation status, mutation in RAS signaling pathway, abnormal expression of flow markers CD13/CD16, HLA-DR/CD13 or CD7 (HR=3.23, [95 CI: 1.90 - 5.49], p=<0.0001). Risk scores were grouped as low risk (score=0), intermediate risk (score=1), and high risk (score ≥ 2), with estimated 1-yr MNFS of 84%, 74%, and 31%, respectively (Figure 2).

Conclusion: CCUS has unique features compared to ICUS. Several factors, including clinical characteristics, immune-phenotyping by FC, and somatic mutations have important impact on risk of progression to MN and on overall survival. Our findings serve as proof-of-concept that such integrated models could help identify CCUS patients at higher risks for progression to MN or death. They can guide treatment accordingly and should be evaluated further.

Disclosures

Shah:Dren Bio: Consultancy.

Author notes

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Asterisk with author names denotes non-ASH members.