One's cognitive behavior (behavior that is caused by cognition, or thinking) can indeed be affected/influenced/caused by a brain tumor, if I am correctly understanding your question.
For example, depending on the location of the tumor, brain tumors can induce schizophrenic (, multiple-personality manifestation, delusional thinking and behaviors/reaction) and psychotic behavior (violence) and behavior that is obsessive/compulsive, etc. This is why psychologists first ask patients for their medical history and date of last phsycial examination before treatment.
For example, depending on the location of the tumor, brain tumors can induce schizophrenic (, multiple-personality manifestation, delusional thinking and behaviors/reaction) and psychotic behavior (violence) and behavior that is obsessive/compulsive, etc. This is why psychologists first ask patients for their medical history and date of last phsycial examination before treatment.