Results from a pre-specified analysis examining rPFS demonstrated a statistically significant improvement in rPFS in the ZYTIGA plus prednisone arm (ZYTIGA arm) compared to the placebo plus prednisone (control) arm. The median rPFS in the control arm was 8.28 months but had not yet been reached in the ZYTIGA arm because progression events were occurring more slowly in the ZYTIGA arm compared to the control arm (N=150 vs. 251, respectively). These results reached statistical significance with a p-value <0.0001 and a hazard ratio (HR) of 0.425 [95% confidence interval (CI): 0.347, 0.522].
Additionally, in a separate pre-specified interim analysis, OS was longer for the ZYTIGA arm compared to the control arm with an HR of 0.792: median overall survival was 35.3 months in the ZYTIGA arm versus 30.1 months in the control arm (95% CI: 0.655 - 0.956). The p-value was 0.0151, which did not meet the pre-specified value for statistical significance.
Treatment with ZYTIGA plus prednisone also resulted in significant improvements in secondary study endpoints compared to the control arm. Specifically, ZYTIGA plus prednisone resulted in improvements in median time to opiate use for cancer pain (the median time in the ZYTIGA arm was not reached and was 23.7 months in the control arm; HR= 0.686; 95% CI: [0.566, 0.833]; p=0.0001); and median time to initiation of cytotoxic chemotherapy for prostate cancer (25.2 months for the ZYTIGA arm vs. 16.8 months for the control arm (HR=0.580; 95% CI: [0.487, 0.691]; p<0.0001).
The most common adverse reactions (greater than or equal to 10%) are fatigue, joint swelling or discomfort, edema, hot flush, diarrhea, vomiting, cough, hypertension, dyspnea, urinary tract infection and contusion. The most common laboratory abnormalities (> 20%) are anemia, elevated blood levels of certain tissue enzymes (alkaline phosphatase, aspartate aminotransferase, and/or alanine aminotransferase), high blood levels of triglycerides (hypertriglyceridemia) and cholesterol (hypercholesterolemia), low levels of immune cells called lymphocytes (lymphopenia), hyperglycemia, and low blood levels of phosphorous (hypophosphatemia) and potassium (hypokalemia).