The problem with chemotherapy and brain cancer is that the chemo medications have a problem getting through the blood-brain barrier.
A friend's mother had a glioblastoma and that was the problem with that cancer. It can usually be treated very successfully with surgery and radiation, but chemo is ineffective, and the radiation and surgery don't usually cure it. A person may remain cancer free for some time, but the tumor almost always comes roaring back, and very aggressively. The radiation and surgery are just buying time.
The lady I'm speaking about was cancer free for about a year. Then she died in about six months, so her total survival was about 18 months after diagnosis. Her oncologist said that chemo had been shown to be very effective in treating those tumors, and research was ongoing to find a way for the meds to cross the blood-brain barrier.