Eisai unveiled new data for its Biogen-partnered Alzheimer's disease therapy Leqembi (lecanemab-irmb), putting forward a case for continuous treatment with the anti-amyloid antibody beyond the initial 18-month period studied in the pivotal Clarity AD trial.Clarity AD, which led to Leqembi's full FDA approval in 2023, had previously demonstrated a 27% slowing of cognitive decline over 18 months compared to placebo, based on Clinical Dementia Rating-Sum of Boxes (CDR-SB).The new findings, presented at the Alzheimer's Association International Conference (AAIC), looked at one set of patients who were administered Leqembi continuously for three years as part of Clarity AD and its open-label extension study, while another group received placebo for the first 18 months before switching to Leqembi for the same duration. Eisai also monitored a separate cohort outside the trial who remained untreated for three years.Cognitive impactLynn Kramer, Eisai's chief clinical officer of deep human biology learning, noted that the difference in cognitive decline between the Leqembi early-starters and those who were untreated throughout the study grew wider. Specifically, after three years, the drug was found to slow cognitive decline by 31% compared to what would be expected in similar patients who did not receive treatment.According to Kramer, the drug "interrupts the natural progression of the disease, and it has an effect more and more."The study included an optional tau PET substudy involving 41 patients with no tau or a low accumulation of tau in the brain, representing an early stage in the disease course. After three years of Leqembi treatment, over half of the patients showed improvement or no decline in cognitive and functional assessments, including 59% on the CDR-SB, 63% on the ADAS-Cog14, and 63% on the ADCS MCI-ADL."This suggests that earlier initiation of treatment with [Leqembi] may have a significant positive impact on disease progression and may provide continued benefits to patients with early [Alzheimer's disease] over the long-term," the company said.ARIA 'low and similar' to placeboMoreover, no new safety issues were found after three years of Leqembi. Eisai said most amyloid-related imaging abnormalities (ARIA) occurred in the first six months and then were "low and similar" to placebo rates. Analyses showed ARIA had no impact on cognition or function, and was not linked to faster long-term progression, it added. The risk of ARIA was one of the safety concerns raised by European regulators last week, who concluded that Leqemb’s benefits are outweighed by the associated serious adverse events.The three-year data release comes amid a shift in the Alzheimer's space with the arrival of a key drug rival. Just weeks ago, the FDA approved Eli Lilly's competing anti-amyloid antibody Kisunla (donanemab-azbt). Unlike Leqembi, which is administered indefinitely, Kisunla's treatment regimen allows for discontinuation once amyloid plaques are cleared from the brain.The difference in approach has become a key point of discussion among experts. In a recent interview with FirstWord, George Grossberg, director of geriatric psychiatry at Saint Louis University School of Medicine, noted that Kisunla's limited-duration regimen "is very attractive," referring to the possibility of stopping treatment after 10 to 12 months if brain scans show amyloid clearance.Drawback of stoppingHowever, Eisai's new data puts up a possible challenge. The company cites data from Study 201, a mid-stage involving early Alzheimer's patients who, following the 18-month core study, participated in an open-label extension after temporarily stopping treatment for two years on average.Eisai's analysis showed that even after amyloid plaques are cleared, Alzheimer's continues to progress when treatment is stopped. Patients who discontinued Leqembi saw their rate of cognitive decline revert to that of untreated patients, suggesting a need for ongoing therapy to maintain benefits, according to the company.Eisai noted that Leqembi is the only widely available early Alzheimer's treatment that offers a dual mechanism targeting both amyloid plaques and protofibrils, which accumulate early in the Alzheimer's brain and lead to nerve cell function loss, abnormal nerve processes, inflammation, and memory loss. “Continuing treatment is important if you would like to maintain cognition and functionality longer,” Kramer said, adding “the concept is, if you stop [treatment], you get worse.”For more, see – Physician Views In-Depth: Though Eli Lilly’s new Alzheimer's treatment is a fast favourite, Kisunla is unlikely to be kiss of death for Leqembi.