WASHINGTON, DC—A small-molecule inhibitor can improve overall survival (OS) in certain patients with previously treated myelodysplastic syndromes (MDS), results of a phase 3 trial suggest.
Overall, patients who received the dual PI3K/PLK pathway inhibitor rigosertib along with best supportive care (BSC) did not see a significant improvement in OS compared to patients who received BSC alone.
However, rigosertib did improve OS in patients with poor prognosis.
Guillermo Garcia-Manero, MD, of the MD Anderson Cancer Center in Houston, Texas, and his colleagues presented these results at the 13th International Symposium on Myelodysplastic Syndromes (abstract 112).
The trial, known as ONTIME, was sponsored by Onconova Therapeutics, Inc., the company developing rigosertib.
The trial included 299 higher-risk MDS patients with excess blasts (5% to 30% bone marrow blasts) who had failed to respond to (25%), progressed on (37%), or relapsed after (38%) treatment with hypomethylating agents (HMAs).
Patients were randomized 2:1 to receive rigosertib plus BSC or BSC alone. Patients treated with rigosertib received 1800 mg every 24 hours for 72 hours as a continuous, intravenous, ambulatory infusion, every 2 weeks for the first 16 weeks, then every 4 weeks.
The treatment arms were generally balanced in terms of baseline characteristics. The majority of patients were male (66%) and white (82%). The median age was 74 years. Most patients (85%) had an Eastern Cooperative Oncology Group score of 0 or 1.
The median duration of the last HMA therapy was 8.8 months for patients in the rigosertib arm and 10.3 months for patients in the BSC arm.
The researchers found no significant difference in OS between the treatment arms. The median OS was 8.4 months in the rigosertib arm and 5.9 months in the BSC arm, and the 12-month OS was 35% and 25%, respectively (hazard ratio[HR]=0.87, P=0.31).
On the other hand, certain patients did see a significant improvement in OS with rigosertib. Among patients with primary HMA failure (those who failed to respond to or progressed during HMA therapy), the median OS was 8.6 months in the rigosertib arm and 5.3 months in the BSC arm (HR=0.69, P=0.040).
For patients who received HMAs for less than 9 months, the median OS was 7.7 months in the rigosertib arm and 4.5 months in the BSC arm (HR=0.55, P=0.003). Among patients younger than 75 years of age, the median OS was 9.7 months in the rigosertib arm and 4.1 months in the BSC arm (HR=0.52, P=0.0004).
And for patients with very high-risk disease according to the Revised International Prognostic Scoring System, the median OS was 7.6 months in the rigosertib arm and 3.2 months in the BSC arm (HR=0.56, P=0.005).
The researchers said there were no obvious differences between the treatment arms with regard to overall adverse events (AEs) or grade 3 or higher AEs.
Overall, 99% of patients in the rigosertib arm and 85% in the BSC arm experienced treatment-emergent AEs. The incidence of grade 3 or higher AEs was 79% and 68%, respectively.
Treatment-emergent AEs of all grades—occurring in the rigosertib and BSC arms, respectively—included nausea (35% vs 18%), diarrhea (33% vs 20%), constipation (31% vs 11%), fatigue (30% vs 18%), pyrexia (27% vs 21%), anemia (23% vs 9%), peripheral edema (21% vs 16%), and thrombocytopenia (21% vs 8%).
Considering the study results together, Dr Garcia-Manero and his colleagues concluded that rigosertib is likely most effective in high-risk MDS patients with the worst prognosis, and these patients can safely receive the drug.
