GTX (GTXI) Reports Two POWER Trials Failed to Meet co-Primary Endpoints

August 19, 2013 8:02 AM EDT
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GTX, Inc. (Nasdaq: GTXI) announced results of its two Phase 3 enobosarm clinical trials, the POWER trials, in patients with non-small cell lung cancer (NSCLC) receiving chemotherapy. The Company announced that the clinical trials failed to meet the overall criteria for the co-primary responder endpoints of lean body mass and physical function as agreed upon with the United States Food and Drug Administration (FDA); the responder endpoints showed mixed results (for POWER1 and POWER2, p values at Day 84 for LBM were 0.036 and 0.113, respectively; p values at Day 84 for SCP were 0.315 and 0.289, respectively).

Initial exploratory quantitative (continuous variable) analysis demonstrated that enobosarm had a consistent effect on LBM relative to placebo in both studies at all assessment times (p values were 0.0003 and 0.0227 at Day 84 for POWER1 and POWER2, respectively). Corresponding analyses for SCP were inconsistent between trials (p values were 0.0336 and 0.7923, respectively). Missing data were well balanced between the arms in both trials for both endpoints.

Across both clinical trials, enobosarm was generally well tolerated, with the occurrence of serious adverse events and overall incidence of adverse events similar across placebo and treatment groups. In POWER1, the four most common adverse events reported (in decreasing order of incidence) were nausea, alopecia, anemia and vomiting. In POWER2, the four most common adverse events reported were anemia, nausea, neutropenia and vomiting. In the safety analysis of survival, there was no evidence of a difference between patients treated with enobosarm and placebo in either clinical trial.

“While we are disappointed that both studies did not meet the pre-specified responder analyses, we are encouraged by the unambiguous effect of enobosarm on muscle and we are confident that it will translate to clinical benefit and potentially increase survival in patients with non-small cell lung cancer,” said Mitchell Steiner, M.D., CEO of GTx. “We look forward to sharing our clinical data from these and previous trials with FDA and European authorities to discuss the path forward. I would like to personally thank all the employees at GTx for their tremendous effort in conducting two high quality Phase 3 clinical studies and the principal investigators and their staff at over 80 clinical sites in 8 countries for their help recruiting and managing these studies. Most of all, I want to thank the patients with non-small cell lung cancer who participated in the POWER1 and POWER2 clinical trials in order to make it possible for future patients to potentially have access to important therapies.”

Published observational data suggest that LBM is related to survival outcome. This observational finding has been replicated based on exploratory analysis of current survival data from the POWER studies using landmark analysis and time-dependent covariate Cox regression modeling that includes LBM response and arm as covariates. The effect size and direction were similar in both trials.

GTx plans to initiate discussions with both the FDA and European regulatory authorities to determine the path forward.

“Muscle wasting in patients with non-small cell lung cancer is devastating and unfortunately it affects hundreds of thousands of patients worldwide,” said Jeffrey Crawford, M.D., Chief, Division of Medical Oncology at Duke University School of Medicine, and principal investigator for the POWER1 and POWER2 trials. “While some of the pre-specified primary endpoints were not met, I am encouraged by the substantial and consistent effect of enobosarm on muscle in these patients with lung cancer receiving chemotherapy.”

“Data from the POWER trials provide compelling evidence that enobosarm maintains or increases muscle,” said Carla Prado, Ph.D., Assistant Professor, Nutrition, Food and Exercise Sciences at Florida State University. “Loss of muscle, independent of weight loss, is a common and often occult feature of cancer, and is acknowledged as a remarkable and powerful prognostic indicator of shorter survival.”

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