ASXL1 Mutations Predict a Poor Response to Darbepoetin Alfa in Anemic Patients with Low-Risk MDS: A Multicenter, Phase II Study

Introduction: Myelodysplastic syndromes (MDS) is thought to develop and progress as a result of accumulation of genetic mutations. This multicenter, open-label, phase II study examined impact of gene mutations on the effect of darbepoetin alfa (DA) for anemia. Death within 1 year and progression to acute myeloid leukemia (AML) were also examined.

Methods: DA ≤240 μg was administered once weekly for 16 weeks to DA-naive, low-risk MDS (low or Intermediate-1 [Int-1] risk defined by the International Prognostic Scoring System [IPSS] risk classification) patients with anemia. DNA was extracted from the peripheral blood of patients, and presence of previously reported high-frequency gene mutations in MDS (SF3B1, TET2, SFRS2, ASXL1, DNMT3A, etc.) was analyzed by next-generation sequencing. Primary endpoint was association between frequently observed mutated genes and therapeutic effect of DA (IWG criteria 2006 (HIE)) at 16 weeks. A secondary endpoint was survival analysis results for death and progression to AML within one year after 16 weeks of treatment, with the date of first treatment as the starting date. For AML, progression to AML and subsequent death were stated as events, and the patients without confirmed progression to AML were censored at the date of last known survival. For overall survival, death from any cause was considered an event, and for the survival cases, the study was terminated at the date of last known survival.

For the primary endpoint, relative risk and 95% confidence intervals (CI) were calculated using Wilson's score method; statistical significance was assessed using Pearson's chi-square test. Multivariate analysis was performed by adding baseline erythropoietin (EPO) levels (low: <91.8, high: 91.8+ [mIU/mL]) to the explanatory variables, and odds ratio was calculated using logistic regression model. Survival curve was estimated using Kaplan-Meier method and median survival time (MST) was calculated using Brookmeyer and Crowley method.

Results: Of the 85 patients enrolled between August 2016 and May 2019, 4 patients who were judged ineligible and 2 patients who discontinued the study prior to the start of treatment were excluded, and 79 subjects were included in the analysis (full analysis set). Of 79 subjects, 52 (65.8%) were male (median age 77.0 [29-90] years). IPSS risk was low in 27 (36.7%) and Int-1 in 50 (63.3%) subjects. The frequently mutated genes (³10%) were SF3B1 (24, 30.4%), TET2 (20, 25.3%), SRSF2 (10 cases, 12.7%), ASXL1 (9, 11.4%), and DNMT3A (8, 10.1%). Overall response rate was 70.9%. Univariate logistic regression analaysis did not show any significant association between these mutations and therapeutic efficacy of DA. The same results were obtained when the analysis was limited to red blood cell transfusion-dependent subjects (n=15). After adjusting against baseline EPO values, mutations of ASXL1 gene were associated with significantly worse response (odds ratio 0.180 [0.035-0.928], p = 0.040).

Six (7.6%) confirmed cases of AML and 17 (21.5%) deaths (death before confirmed AML) were observed. Overall, 21 deaths were observed including 4 deaths after progression to AML. The median survival time (95% confidence interval) from the start of treatment to confirmed AML or death was 41.3 months (30.6 months - Not reached).

Conclusions: The results of this exploratory study suggest that the presence of ASXL1 gene mutations may result in poor response to the anemic treatment with DA in low-risk MDS. The current analysis of progression to AML and death included subjects whose observation period did not reach the prespecified number of days. For such cases, the outcome research will be conducted around October 2020 and updated results will be presented at the ASH 2020 conference.