For what length of time can someone live with a brain tumor without treatment?

Depends on Type: The pathology and location both effect the prognosis of brain tumors. Small benign tumors can be monitored and will not effect survival. Aggressive tumors, such as grade 4 astrocytomas, have a poor prognosis even with aggressive surgical resection. The location of the tumor is important because the closer a tumor is to critical structures the more dangerous it can be.

Depends: It depends on what kind of tumor you have. Glioblastoma multiforme (gbm) is the most aggressive kind and you have a 3-6 month survival without treatment. Some meningiomas you can live just as long if you have no treatment and they are small.