Analyst response to results from PRIME study of aducanumab for mild Alzheimers disease-Biogen

Analyst and professional response to the announcement by Biogen of new results from the Phase Ib PRIME trial of aducanumab for mild Alzheimers disease was muted. Data was presented at the AAIC meeting and showed that patients treated with up to 52 weeks with a 6 mg/kg dose of the drug demonstrated acceptable safety and tolerability and reinforced previous results showing a significant reduction of beta amyloid in the brain and improvement of clinical decline as measured by Mini Mental State Examination (MMSE) and Clinical Dementia Rating scale- sum of boxes (CDR-SB) but not a reduction that was statistically significant but was seen by Biogen as dose dependent.

Analysts noted that the 6 mg/kg dose did worse than the 3 mg/kg dose arm on the MMSE scale demonstrating a distortion of data that questioned the dose dependency assertion. It was also noted that patients on the 6 mg/kg dose who did not carry the Apo E4 genetic risk factor suffered an ARIA-E (amyloid related imaging abnormalities-brain swelling) of 22% which was double that of the earlier announcement.In Apo-E4 carriers the incidence of ARIA-E was 5% in 1mg/kg and 3 mg/kg arm and 43% in the 6 mg/kg arm and 55% in the 20 mg/kg arm.

Biogen has commented that the trial was a small study powered on changes in PET imaging not clinical outcomes and were encouraged by the results and confirmed that the company will proceed into Phase III with ENGAGE and EMERGE trials for mild Alzheimers disease.