Efficacy and Safety of Eltrombopag for Treatment of Patients with Myelodysplastic Syndromes after Hypomethylating-Agent Failure: A Phase 2 Clinical Trial

Background: Myelodysplastic syndromes (MDS) are malignant clinical disorders characterized by ineffective hematopoiesis, bone marrow dysplasia, peripheral cytopenias and a property to transform into acute myeloid leukemia (AML). Standard of care for MDS includes the hypomethylating agents (HMAs) (i.e. azacitidine, decitabine) to improve quality of life, decrease transfusion requirements and improve clinical outcome. However not all patients (pts) respond to HMAs and even in responding pts, cytopenias may persist. HMA-failure MDS has extremely poor prognosis and currently there are no approved therapeutic options for such pts who are often of advanced age with frequent comorbidities.

Objectives: The dual primary objectives of this study evaluate the safety and efficacy of the second-generation thrombopoietin-receptor agonist (TPO-RA) eltrombopag (EPAG) for the treatment of MDS pts at the time of HMA-failure. Secondary objectives include incidence of transformation to AML and evaluation of bone marrow fibrosis during therapy.

Methods: Eligible pts for this 2-arm phase 2 open-label clinical trial included adults with MDS after completing >4 HMA cycles with failure to achieve at least a partial response, or the presence of ongoing cytopenias per IWG criteria. Arm A includes eltrombopag monotherapy and Arm B includes eltrombopag with continuation of the HMA at the previous dosing schedule. The starting eltrombopag dose is 200mg orally daily, which can be increased to 300mg in the absence of toxicity. First response is assessed after 2 cycles with each cycle lasting 28 days. The primary efficacy endpoint was overall response rate based on the IWG-2006 criteria.

Results: To date, 23 pts with a median age of 72 years (range 42-84 years) have been enrolled. Prior to study entry, pts had received a median of 6 (range 4-25) HMA cycles. Cytogenetics were diploid in 12 (53%), intermediate in 7 (30%), and high risk in 4 (17%) pts by IPSS. Median bone marrow blasts at study start was 3% (range 0-15%). Arm A has enrolled 7 pts with a median age of 74 years; Arm B has enrolled 16 pts with median age of 69 years. In Arm B, ongoing HMA therapy includes azacitidine in 7 (44%) and decitabine in 9 (56%). Nine (39%) pts increased to 300mg EPAG after median of 8 weeks on study. Median total cycles received on study is 5 (1-17); median OS has not been reached.

Overall, 16 pts are response-evaluable; 7 pts discontinued prior to the first response assessment at 2 months (4 due to AEs including myalgias/fatigue (n=2), hyperbilirubinemia (n=1), and pneumonia (n=1), 2 per pt request and 1 for pt inability to comply with protocol requirements). Of the 16 response-evaluable pts, 3 (19%) in Arm B demonstrated platelet improvement, including one pt necessitating EPAG dose-reduction to 100mg due to platelet count exceeding 450 x10⁹/L with concomitant ANC recovery at 200mg EPAG dose level. An additional 8 (35%) pts have remained on study for a median of 5 cycles (2-17) with stable disease. Two pts discontinued therapy due to disease progression, including 1 (4%) that progressed to AML. The most common non-hematologic AEs regardless of attribution included hyperbilirubinemia (n=14, 61%), fatigue (n=13, 56%) myalgias (n=11, 48%), fever (7, 30%), dyspnea (7, 30%), nausea (6, 26%) and transaminitis (4, 17%). No significant increase in bone marrow fibrosis has been observed.

Conclusion: Eltrombopag orally daily appears to be a safe and beneficial supportive adjunct for pts with MDS while receiving HMA-therapy or after HMA-failure due to persistent cytopenias. Treatment on this study continues and larger prospective clinical trials are needed to confirm these preliminary findings.