Doctor scared my son talking about him having brain tumor. what would you say?

BRAIN TUMOR: Brain tumor can be benign or malignant, also the prognosis depends on the location of the tumor. Currently a lot of advaned ways help in dianosis and treatment and the long term survival improved significantly compared to what was many years ago.

Important discussion: I'm sorry your son (and you?) are frightened, but his physician must be concerned about symptoms present, physical exam findings, or MRI scan or other diagnostic test results. I'd suggest listening carefully to what's recommended for further investigations, and carrying these out. Most physicians don't purposefully scare people, but do emphasize need for appropriate care & treatment.