you poor thing and your poor friend, i hope you're both ok.
if it makes you feel any better, about 5 years ago we had a call and found out our friend had a brain tumour too, was an awful time. but she's totally fine now. they've never operated and they don't know for sure if it's cancerous or not, but she's on daily medication and they monitor it so it doesn't grow and *touch wood* so far so good, she got married last year and is currently honeymooning in thailand.
try and keep a strong positive outlook and i hope it's all ok x