Are all brain tumors fatal?

No, very variable: While some brain tumors are extremely dangerous, others are often quite benign and do not require removal unless they are causing symptoms.

GBM?: GBM has a grave prognosis despite surgery, radiation, or chemotherapy. It is the most common primary brain tumor. Other brain tumors are benign (not cancerous) and are associated with good survivability. Surgical biopsy by a neurosurgeon should be considered.

Not at all: There are numerous types of brain tumors, and some are benign, others are malignant. You need to know exactly what kind of tumor it is to assess likelihood of it being 'fatal.' Even if malignant, tumors can be treated and patients can survive for a period of time. Some brain tumors (meningioma, pituitary Adenomas) are usually quite benign and treatable.