On June 10, 2015 OncoGenex Pharmaceuticals reported that the U.S. Food and Drug Administration (FDA) has agreed to the Company’s proposed amendment to the Phase 3 AFFINITY protocol and statistical analysis plan (Press release, OncoGenex Pharmaceuticals, JUN 10, 2015, View Source [SID:1234505390]). The amendment includes the addition of a co-primary endpoint designed to prospectively evaluate the survival benefit of custirsen in men who are at increased risk for poor outcomes when treated with cabazitaxel for metastatic castrate-resistant prostate cancer (CRPC).
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"There are limited effective treatment options for men with metastatic CRPC who have risk factors for poor outcomes and who fall into a poor prognosis category. Recent findings from the SYNERGY trial showed a significant survival benefit in this group of patients," said Cindy Jacobs, PhD, MD, Chief Medical Officer and Executive Vice President of OncoGenex. "We have applied this key insight from the SYNERGY trial to the AFFINITY protocol to better evaluate this vulnerable subpopulation of men who have poor prognosis and shorter survival time."
The FDA is in agreement with plans for prospectively defining a poor prognostic subpopulation in the Phase 3 AFFINITY trial. OncoGenex, in collaboration with study investigators, has defined a simple 5-criteria characterization for poor prognosis in prostate cancer based on the Phase 3 SYNERGY trial, which includes: poor performance status, elevated prostate specific antigen (PSA), elevated lactate dehyrdogenase (LDH), decreased hemoglobin, and the presence of liver metastasis. Patients with poor prognosis will be identified as having 2 or more of these 5 well-recognized high-risk criteria. The proposed change for AFFINITY is also consistent with custirsen’s mechanism of action, since custirsen was designed to address treatment resistance which may be more prevalent in this subpopulation.
In the revised statistical analysis plan for the AFFINITY trial, the hypothesized hazard ratio (HR) for the poor prognosis subpopulation is specified to be 0.69 with the critical HR ≤ 0.778. The hypothesized HR for the intent-to-treat patients (ITT population) remains unchanged as 0.75 with the critical HR ≤ 0.820.
Timing for the final analysis of the poor prognosis subpopulation is projected to occur by the end of 2015, while the final analysis for the ITT population is projected to occur in the second half of 2016. FDA and OncoGenex have further agreed that an interim analysis will occur for the ITT population when the final analysis for the poor prognosis subpopulation occurs. This interim analysis will have both futility and early efficacy criteria defined for the ITT population. If the earlier final analysis on the poor prognostic subpopulation shows a survival benefit for custirsen, OncoGenex could initiate a regulatory submission. The entire trial could also be stopped early due to efficacy based on the interim assessment for the ITT population by the Independent Data Monitoring Committee (IDMC).
"Findings from the SYNERGY trial recently presented at ASCO (Free ASCO Whitepaper) have provided important insight into the patient population in whom custirsen treatment is most relevant," said Scott Cormack, President and CEO of OncoGenex. "We are pleased that the FDA has agreed with our amendment and look forward to announcing top-line results at the end of this year and in 2016."
OncoGenex has also initiated a review with the European Medicines Agency (EMA) for the proposed amendment to the Phase 3 AFFINITY protocol and statistical analysis plan, and expects to have this completed in the second half of 2015.
A retrospective analysis of data from the Phase 3 SYNERGY trial recently presented at the 51st Annual Meeting of the American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) showed a benefit with custirsen therapy when added to first-line docetaxel chemotherapy in men with metastatic CRPC who had a poor prognosis. The analysis showed that over 40 percent of men in the trial had at least 2 of the 5 common risk factors for poor prognosis as stated above. In these men, the analysis found a 27 percent lower risk of death when custirsen was used in combination with first-line docetaxel compared to docetaxel alone.
AFFINITY is being conducted at 95 global clinical trial sites and earlier this year, the IDMC recommended the trial continue following the completion of an interim futility analysis. The trial is fully accrued, and the protocol amendment does not affect the conduct of the study.