Estybon mixed results in Phase III trial for Myelodysplastic Syndromes - Oncanova+ Baxter

Onconova Therapeutics, Inc has announced that the Phase III ONTIME trial of intravenous (IV) Estybon (rigosertib) in patients with higher risk Myelodysplastic Syndromes (MDS) who had progressed on, failed or relapsed after prior therapy with hypomethylating agents (HMAs) did not meet the primary endpoint of overall survival compared to best supportive care (BSC). The ONTIME trial enrolled 299 patients including 199 patients in the IV rigosertib plus BSC arm. Median overall survival in the IV rigosertib plus BSC arm was 8.2 months compared to 5.8 months in BSC only arm. Treatment with IV rigosertib plus BSC did not demonstrate a statistically significant improvement in median overall survival when compared to BSC only (Hazard Ratio=0.86; p-value=0.27).

However, a post-hoc analysis demonstrated a statistically significant increase in median overall survival in the subset of patients who had progressed on or failed previous treatment with HMAs (i.e., had not responded to HMAs), thus demonstrating potential activity of rigosertib in these MDS patients. In this subset of patients (184 of 299 enrolled patients), the median overall survival was 8.5 months in the IV rigosertib plus BSC arm compared to 4.7 months in BSC only arm (Hazard Ratio=0.67; p-value=0.022). Among this patient population, 127 patients were in the treatment arm, and 57 patients were in the BSC arm. The other subset which was comprised of patients who had relapsed after responding to previous treatment with HMAs (115 of 299 patients enrolled), did not show a statistically significant survival benefit. Additional analysis is underway to identify potential survival benefit in other subsets of patients. Preliminary safety analysis indicates that rigosertib was generally well tolerated in the study population.