Insights into clonal and CBC changes at disease evolution among ccus patients

Abstract

Abstract Background: Clonal cytopenia of undetermined significance (CCUS) is defined as clonal hematopoiesis in the absence of a hematologic neoplasm, along with unexplained cytopenia. While several studies have identified risk factors and developed scores to predict progression to overt myeloid neoplasms, the clinical and molecular features during the progression process remain poorly understood. Aim: Evaluate the clinical and clonal characteristics of patients with CCUS, with a focus on the longitudinal evolution of clonal and clinical parameters over time. Methods: After IRB approval, we retrospectively reviewed charts of patients with unexplained cytopenia (2015-2024), recording data at the time of CCUS diagnosis (WHO 2022 diagnostic criteria) and at time of follow-up bone marrow biopsy after diagnosis. Follow-up CBC and karyotype data were recorded for patients who had repeat bone marrow biopsies (n= 111), while follow-up clonal parameters and risk scores were calculated for those who underwent repeat NGS (n= 74). A reduction or expansion in clone size was defined as a change exceeding 5% (CE5%), or change exceeding 10% (CE10%) from the baseline value. Overall survival (OS) was calculated from diagnosis to last follow-up. For statistical analysis, we used BlueSky Statistics V10.3.1. Results: 214 CCUS patients (median age 73, 68% males) were included. At baseline, 30% of patients had abnormal cytogenetics, with del (20q) being the most common one (8%; n= 18), followed by trisomy 8 (6%; n= 13), and loss of chromosome Y (5%; n= 10). The median number of mutations was 2 (range, 1-5), with the most common mutations TET2 (38%), SRSF2 (21.5%), ASXL1 (21%), ZRSR2 (18.5%), DNMT3A (9.5%), and U2AF1 (9%). Most patients had high risk CHRS (60%), followed by intermediate (30%), and low risk (10%). On the other hand, 41% had high risk CCRS, 29% had intermediate risk, and 30% had low risk. After a median follow-up of 46 months, 62 patients died (median OS not reached). A decrease in the white blood cell (WBC) count from the time of diagnosis to follow-up was more frequently seen among CCUS patients who progressed to MN (70% vs 50%, p= 0.04), however, changes in hemoglobin and platelets did not differ between those who progressed and those who did not (p> 0.05). Although the frequency of abnormal karyotypes at diagnosis was similar between patients who eventually progressed (28%) and those who did not (31%) (p= 0.6), 4 (2%) patients with initially normal karyotypes acquired chromosomal abnormalities during follow-up, and all progressed to MDS. Among the 74 patients who had follow-up NGS, 31% acquired new mutations, clonal expansion of pre-existing mutations were seen in 54% using CE5% and 19% per CE10%, and 16% developed new variants of uncertain significance (VUS). Acquiring new pathogenic mutations was similar in patients who progressed to MN compared to those who did not progress (34% vs 28%, p= 0.6). On the other hand, clonal expansion was significantly more observed in patients who progressed compared to those who did not, using both CE5% (73% vs 31%, p = <0.001) and CE10% (27% vs 9%, p= 0.03). At follow-up, ASXL1 was the most commonly acquired mutation among patients who did not progress (4 cases), followed by TET2 (2 cases), and U2AF1, GATA2, DNMT3A, SF3B1, ZRSR2, TP53, and CBL (1 case each). On the other hand, SRSF2, SETBP1, CBL, JAK2, TET2, and RUNX1 were more frequently acquired among those who progressed to myeloid neoplasms (each appeared in 2 patients). When recalculating CCRS, CHRS, IPSS-M, and IPSS-R at follow-up for patients who had repeat NGS, there was no significant difference in score changes - either upward or downward - between those who progressed and those who did not (p> 0.05). Conclusion: In CCUS patients who progressed to myeloid neoplasms, WBC decline, clonal expansion (more frequent), and evolving chromosomal aberrations (less frequent) were observed, supporting the value of longitudinal genomic and clinical monitoring in CCUS.