Can the life span of a person who has a brain tumor cancer be measured?

Too many factors: To answer that question here. The type of tumor, tumor aggressiveness, whether its a primary brain tumor or metastasis, and other medical conditions of the patient all play into that calculus. Your neurosurgeon or oncologist may be able to give you some general guidelines.

Yes: Average survival rates can can be given for the most common forms of brain tumors, but they are averages and some people survive longer and some shorter.