Researchers have discovered an explanation for why cerebral cavernous malformations (CCMs)—clusters of dilated blood vessels in the brain—can suddenly grow to cause seizures or stroke. Specifically, they found that a specific, acquired mutation in a cancer-causing gene (PIK3CA) could exacerbate existing CCMs in the brain. Furthermore, repurposing an already existing anticancer drug showed promise in mouse models of CCMs in improving brain-vascular health and preventing bleeding into the brain tissue.