Biogen enrollment increase is not unusual, says William Blair
William Blair analyst Matt Phipps believes increasing enrollment of Biogen's Phase III trials of aducanumab in prodromal Alzheimer's disease to ensure appropriate powering and confidence interval error margin, which caused yesterday's share selloff, is "prudent and not unusual." Based on his analysis, the trial is sufficiently powered to detect a benefit significantly below what was observed in the Phase Ib trial. The increase in variability in and of itself does not preclude trial success, Phipps tells investors in a research note. He sees "very limited" downside at current price levels if aducanumab were to fail, and adds that success of Biogen's growing earlier stage pipeline has the potential to provide additional upside. The analyst sees upside potential of over 50%, to $500 per share, if Phase III trials of aducanumab are successful, and a base support level slightly below $300 per share if the trials fail. Phipps keeps an Outperform rating on Biogen.