How common is it to survive for 3-5 years after being diagnosed with glioblastoma multiforme?

Rare. 5 year life expectancy for glioblastoma multiforme is about 5%.
Uncommon. Some patients do survive for long periods after glioblastoma but the majority have recurrences and the average survival is between 1 or 2 years. However each case is different and how any one person responds to treatment is the determining factor in each case.