The oncology drug cladribine, which is also approved for treatment of multiple sclerosis, could have amyloidogenic effects when administered long term, a study in mice has shown. In a mouse model of Alzheimer disease, 60-day treatment with cladribine more than doubled amyloid plaque burden in the brain. Such changes seemed to be driven by increased turnover of amyloid precursor protein. Moreover, like other cancer drugs, chronic cladribine treatment in mice was associated with deficits in learning skills. These findings highlight the need to monitor possible adverse neurological effects in patients receiving cladribine.