Post-remission clonal hematopoiesis; Practical implications for measurable residual disease assessment in acute myeloid leukemia (AML)

7529 Background: Clonal Hematopoiesis may persist following complete remission (CR) in patients with acute myeloid leukemia (AML) but does not necessarily indicate residual AML and may represent persistence of pre-leukemic stem cells. Post-remission CH identified by NGS has not been systemically studied in parallel with measurable residual disease (MRD) detection by flow cytometric immunophenotyping (FCI). Methods: We studied bone marrow sample from AML patients at baseline and CR by targeted deep NGS of 295 genes (median 403x depth) and compared the results to FCI. Measurable residual disease (MRD) detection by FCI was performed by comparing the phenotype at CR to baseline and by detection of leukemia associated immunophenotype (LAIP) and derivation from normal (DFN) (sensitivity: 0.1%). Post-CR CH was defined as presence of mutations originally detected in AML with variant allele frequency > 2.5%. FCI results were categorized into 4 groups: a) AML MRD negative by LAIP or DFN b) AML MRD+ (similar to baseline) c) AML MRD+ (different from baseline), d) Negative for AML MRD, but aberrant phenotype suggestive of pre-leukemic cells. We correlated FCI and NGS results. Results: 101 patients were included in the study. 45 (45%) had persistent post-CR clonal hematopoiesis; 23 (51%) had phenotypic alterations detected by FCI including AML MRD+ in 18 (40%) and pre-leukemic cells in 5 (10%). Among patient with no detectable mutations by NGS (n = 56; 55%), 14 (25%) had FCI aberrancies including AML MRD+ in 4 (7%) and pre-leukemic cells in 10 (18%). CH was significantly more common in samples with residual phenotypic aberrancies detected by FCI (p = 0.004). There was no significant correlation between FCI group d and persistent CH (p = 0.4). Persistent ASXL1 (p = 0.024, OR = 7.2 ) and RUNX1 (p = 0.016; OR = 17.3) mutations were significantly associated with FCI abnormalities. The correlation coefficient between FCI abnormalities and RUNX1 mutations inferred from a Bayesian network structure was 0.66. Conclusions: NGS and FCI are complementary in evaluating post treatment disease status in AML. Post CR-CH is associated with phenotypic abnormalities that either represent residual AML or pre-leukemic cells. The latter may not have the same prognostic implications as AML MRD; however, the association with outcome needs to be elucidated. Single cell DNA sequencing technologies may be helpful in more accurately deciphering the association of individual gene mutations and their contribution to phenotypic aberrations.