On 4 December, Eisai and Biogen announced that new data on lecanemab in early Alzheimer’s disease (AD) were presented at the 18th Clinical Trials on Alzheimer's Disease (CTAD) Conference in Boston. Data presented were from the Phase III Clarity AD open-label extension along 16 clinical studies of monoclonal antibodies for AD to estimate long-term AD progression over 10 years and the slowing effect of continued lecanemab treatment. Findings suggest that early initiation and long-term lecanemab treatment may continue to slow AD progression and help maintain cognitive function over a longer period. For untreated participants, progression from Mild Cognitive Impairment to moderate AD was 10.1 years, whereas with continued lecanemab treatment, this extended to 13.6 years, indicating a time savings of 3.5 years.
In the low amyloid group, long-term treatment suggested potential to delay disease progression from Mild Cognitive Impairment to moderate AD by up to 8.3 years. Furthermore, according to the companies, each additional year on treatment could further delay disease progression compared to stopping treatment, even long after plaque is expected to have been cleared. Additionally, a scientific symposium at CTAD reported new data on a subcutaneous formulation of lecanemab, which was approved for maintenance treatment in the United States in August 2025. The subcutaneous formulation (500 mg) was tested in a subcohort in the Clarity AD trial open-label extension and demonstrated bioequivalence in drug exposure compared to intravenous dosing of 10 mg/kg every two weeks. Additionally, safety data, including rates of ARIA-E (amyloid-related imaging abnormalities), were comparable between subcutaneous and intravenous administration.