Researchers in South Korea have found that IDH-mutant glioma, one of the most common malignant brain tumors in young adults, can begin years before the tumor shows up on imaging tests. This tumor, which is long-term treated by removing visible tumor tissue, actually occurs when normal-looking brain cells acquire a cancer-associated mutation and spread through the cerebral cortex. Using advanced genetic mapping and animal models, scientists have traced the origin of cancer to glial progenitor cells that appear healthy at first glance. These cells silently mutate and lead to tumor development.