My dad had a recurrence at the end of July and although there were some noticable differences - loss of some fine motor skills, not big deal. And then in a period of 4 days went from walking slowly by himself, to needing some help, to a walker and finally a wheelchair. New MRI and no growth so they did reduce his medications. Problem is that with everything else going on, that was too late and he is now in a hospice but they suggested it could well have gone the other way and in a positive direction.
They attributed the rapid decline to "UNDERLYING" causes and his GP who has been deeply involved basically admitted that was shrugging of the shoulders and saying that they did not have a clue. I was in the room and the look of puzzlement was real as was it after they took his file in front of a multidisciplinary committee. Or another way, stuff happens and sometimes it is bad and sometimes it is good.
And to illustrate this - across the room from my dad's is a 59 year old with the same brain cancer. They put him in as he only had a week or two to live and that was seven weeks ago. He stopped eating and drinking, family flew in, goodbyes were said and yesterday, he suddenly pepped up and ate a big dinner. Good to remember that there are essentially nothing more than educated guesses and it is also good to question the experts.