Glioma development: where did it all go wrong?

Investigating the family tree of a tumor to identify its cellular origins is a daunting task. Liu et al. (2011) now use an elegant lineage tracing technique (MADM) to visualize glioma from its earliest stages. They show that mutations originally induced in neural stem cells lie dormant and only trigger malignant transformation following differentiation into oligodendrocyte precursor cells.