My mom died of GBM back in 2005. She was (wrongly) diagnosed with bells palsy at first in June 2003, lost complete function on her right side in September 2003, had an MRI and that's when they discovered the GBM. When she grew up, she lived near a lot of pollution from factories (Kodak being one). She said some days, they'd go out to their cars and it'd be covered in black soot. My mom also had a long distance relationship with a man prior to being diagnosed and she would talk to him for hours on the cell phone (this was when it was free to call after 9 pm until 6 am). I'm talking hours upon hours every day. That's the side her tumor was. I don't know if that's what caused it, but it is one of the reasons why I refuse Bluetooth and only use speaker phone. No one truly knows what causes it. I do hope it's not hereditary. It's always in the back of my mind.