So your DNA is supposed to be in your chromosomes but when your cells are damaged some of the DNA forms these little circles called plasmids

https://en.wikipedia.org/wiki/Extrachromosomal_DNA

this causes the cell cycle to go bonkers and thus you get cancer. Glioblastoma is a super aggressive cancer that is hard to treat so any progress on it is important.

Cancer is usually not just one mutation because there are multiple checks on the cell cycle and this study finds the ecDNA appeals in cells before they are cancerous which opens the possible of early detection and early treatment.