Emergence ofNPM1Wild-Type Myeloid Neoplasms after Chemotherapy for Acute Leukemia withNPM1Mutation: Proposed Mechanisms of Clonal Evolution
Authors: Castaño-Díez Sandra , Lopez-Guerra Monica , Guijarro Francesca , Bataller Torralba Alex , Esteban Daniel , Castillo Carlos , Jiménez-Vicente Carlos , Charry Paola , Dolors Colomer , Rozman María , Esteve Jordi , Diaz-Beyá Marina 
Published: February 2021

Introduction
NPM1mutation is considered a founder genetic event of acute myeloid leukemia withNPM1mutation (NPM1mut-AML). Nonetheless, growing evidence of pre-existing genetic mutations and clonal hematopoiesis (clonal response) after intensive AML treatment in many patients is being generated, although the precise clinical impact of this genetic background is mostly unknown. Thus, the emergence of a wild-typeNPM1myeloid neoplasm (NPM1wt-MN) after intensive chemotherapy treatment forNPM1mut-AML is a well-known phenomenon, but poorly described in long-term follow-up. Sequential genetic analysis with next generation sequencing (NGS) has the potential to elucidate the clonal origin of diverse emerging clinical scenarios occurring during clinical follow-up based on tracking of genetic evolution of clonal hematopoiesis status after AML treatment, as recently proposed (Hasserjian et al, Blood 2020). We aimed to analyze the incidence and clinico-biological characteristics ofNPM1wt-MN emerging after treatment forNPM1mut-AML in a long-term follow-up series from a single institution.
Patients and Methods
We included in the study 62 patients diagnosed withNPM1mutAML patients and treated with intensive chemotherapy according to two consecutive protocols of the Spanish CETLAM cooperative group (CETLAM-2003 and -2012). Patients were diagnosed between 2005 and May 2019.NPM1wt-MN has been classified according to recent criteria proposed by Hasserjian et al, Blood 2020. Statistical analyses were performed using Rv3.1 and SPSS v20. Next generation targeted sequencing (NGS) was performed with Ion Ampliseq AML Research and Oncomine Myeloid Research Assay panel.
Results
The cohort included 62 patients (median age, 53 years, 25-73) with a median follow-up of alive patients of 44 months. After induction therapy, 58 patients (pt) achieved complete remission (CR) and 21 pt relapsed asNPM1mut-AML. Additionally, 9 pts (15%) developed aNPM1wt-MN: 4 (7%) presented aNPM1wt-AML relapse and 5 (8%) developed otherNPM1wt-MN (non-AMLNPM1wt-MN) that would be classified as residual myeloid neoplasm according to proposed criteria: 1 myelodysplastic syndrome, 3 myeloproliferative/myelodysplastic syndrome [2 CMML and 1 atypical chronic myeloid leukemiaBCR-ABLnegative (aCML)] and 1 polycythemia vera (PV)
Characteristics of the 3 groups (NPM1mut-AML,NPM1wt-AML, non-AMLNPM1wt-MN) are shown in the Table. Median time from CR achievement to progression was longer in the group who developed a non-AMLNPM1wt(24 vs 8 months; p=0.016), and an statistical trend of younger ager in pts with AML-NPM1mutgroup (48 vs 69 vs 60 years-old, respectively, p=0.056) and lower leucocyte count in pt presenting a non-AMLNPM1wt-MN (5.5 vs 29 vs 50 x109/L, respectively, p=0.065) were observed. Moreover, among 19 pts with available NGS at diagnosis,DNMT3Amutation was more frequently comutated inNPM1mut-AML (71% vs 0%vs 40%, respectively p=0.034) andSRSF2was more frequently mutated in non-AMLNPM1wt-MN (60% vs others (0%), p=0.01). Interestingly, outcome of patients presenting with AML relapse did not differ according to NPM1 status at relapse (NPM1mut-AML vs.NPM1wt-AML), with a similar response rate after salvage chemotherapy (80% vs 75%, p=NS) and OS (5-year OS: 75±40% vs 60±20%; p=NS).
NGS analysis of paired samples at diagnosis and emergentNPM1wt-MN in pts who lostNPM1mutation at progression is detailed in Figure. Frequently persisting mutations were those usually found in clonal hematopoiesis such as DNA methylation (TET2, DNMT3A, IDH1, IDH2), chromatin remodeling ASXL1, and splicing factor SRSF2, whereasFLT3mutation was the most frequently lost at relapse.TP53, PTPN11,SETBP1, JAK2, IDH1oASXL1were mutations gained at time of NPM1wt-MN emergence.
Conclusions
A proportion of pts withNPM1mut-AML will develop an NPM1 wild-type myeloid neoplasm after intensive chemotherapy-induced CR, emerging from preleukemic clonal hematopoiesis. Given this possible evolution, which can not be predicted byNPM1mutmeasurable residual disease monitoring, an active surveillance of these pts is recommended, including genetic re-testing at time of disease relapse or progression.
Acknowledgement:PI16/01027 (JE; MDB), PI19/01476 (JE; MDB)
Table:Characteristics at diagnosis depending on type of progression.
Figure:Mutations in paired samples (diagnosis/relapse) of patients who developed aNMPwt-MN.
Figure

Disclosures
No relevant conflicts of interest to declare.