Acute myeloid leukemia exhibiting clonal instability during treatment: Implications for measurable residual disease assessments.

• Changes in the clonal composition of acute myeloid leukemia occur during therapy. • Rare cases of outgrowth of clones related to nonmalignant, but clonal hematopoiesis unrelated to the leukemic clone can be seen on regeneration after chemotherapy. • In cases in which changes occur in the proportions of leukemic subclones, the largest subclone is not necessarily the one with relapse-initiating potential. • Caution is warranted when correlating residual disease levels to prognosis in patients whose leukemic subclones exhibit differential responses to chemotherapy. • It remains to be seen whether these findings can be extrapolated to the minimal residual disease setting when overall reduction of leukemic subclones is much greater. Next-generation sequencing (NGS) is an excellent methodology for measuring residual disease in acute myeloid leukemia and surveying several subclones simultaneously. There is little experience with interpretation of differential clonal responses to therapy. We hypothesized that differential clonal response could best be studied in patients with residual disease at the time of response evaluation. We performed targeted panel sequencing of paired diagnostic and first treatment evaluation samples in 69 patients with residual disease by morphology or measurable residual disease (MRD) level >0.02. Five patients had a rising clone at the time of evaluation. In a representative case, the rising clone was present only in the putative healthy stem cells (CD45lowCD34+CD38–CD123–CD7–) and not in the putative leukemic stem cells (CD34+CD38–CD123+CD7+) cells, thus indicating nonmalignant clonal hematopoiesis. In contrast, 17 of 43 evaluable patients exhibited a differential response in genes related to the leukemic clone. Twenty-six of 43 patients exhibited a clonal response that followed the overall treatment response. Patients with a differential response had better event-free survival (EFS) and overall survival (OS) than those in whom the clonal response followed the overall response (log-rank test, EFS: p = 0.045, OS: p = 0.050). This indicates that when following multiple leukemia-related clones, the less chemotherapy-responsive clone could, in some cases, have lower relapse potential, contrary to what is known when using standard mutation or fusion transcript-based disease surveillance. In conclusion, our results confirm the potential of refining MRD assessments by following multiple clones and warrants further studies on the precise interpretations of multiclone NGS–MRD assays. [ABSTRACT FROM AUTHOR]