Limited symptomatic side effects of brain swelling – amyloid-related imaging abnormalities-edema/effusion (ARIA-E) – were noted in 2.8% of patients in the lecanemab treatment group, which the companies state was within expected levels. Full trial results will be published later in the month, but this news has been welcomed by medics, scientists and patients. These gains have been hard won, with so many drug trials failing, that questions were beginning to be raised about whether amyloid beta was really the cause of the disease. However, this study shows that removal of aggregated amyloid beta in the brain is associated with a slowing of decline in patients at the early stage of the disease, confirming the link between amyloid beta plaque development and disease progression. For this study, patients with mild cognitive impairment due to AD were chosen and amyloid pathology was confirmed by PET, which allows the selection of patients who are at a stage in the disease process where anti-amyloid therapy will be effective. If lecanemab becomes an approved AD therapeutic, wouldn’t it be nice to have a blood- or CSF-based biomarker to help to identify which patients to send for a PET scan?