Brainsem tumor

My son who is now 16 was diagnosed at the age of 4 with a low grade brainstem tumor. It began needing treatment at the age of 9. the tumor will grow, we treat and it stops. then will grow again usually about 18 months later. (after the stop of chemo) Because it is right at the base of the brainstem, where it meets the brain surgery is out of the question.
My question is, can these types of tumors affect behavior? I have been told no, but then yes and in my opinion it seems to affect his behavior, as he gets more aggressive and does things he knows are wrong but can't seem to help. I notice an increase when he has growth in the tumor. This is really frusterating and had to send him to live with his father as I couldn't deal with his behavior any longer as he was rather aggressive. He does have NF 1 as I do. I understand NF can cause probles with behavior as well. BUt as I said I can always tell when the tumor has grown by the way he acts. IE outbursts,becomes aggressive,tires easily.

The first bit of chemo was carboplatin/vinchristine (18 months0 the second was Temozolimide which after 9 months (half the course) was stopped as it was found to increase the chances of Lukemia in NF patients. The next time around my ex decided against treatment as the growth was slight. But now I think it has increased again.