The article talks about the use of external control groups specifically for rare diseases such as Glioblastoma. and shows that the more prognostic characteristics that are controlled for the better the results. I recently wrote about xCures' new xUTILITY program - which creates external control groups with all known prognostic characteristics accounted for! This can be used both for single arm trials as well as randomized trials as described in the current paper!
Disclaimer: I am a founder of xCures, own stock in xCures and am a paid consultant for xCures!