At this time, there is no true cure (100% remission) for brain tumors in dogs (or any species for that matter.) In practice, brain tumors are generally considered to be malignant due to the delicate and poorly regenerative nature of neurons and restriction of the brain to the finite space of the cranium which does not allow tumor growth devoid of collateral damage to brain parenchyma. Therefore, general long-term prognosis for canine brain tumors is poor. Current treatment of brain tumors revolves around four main modalities: surgery, radiation, chemotherapy, and palliative (pain relieving) care. Depending on the type, extent, and location of the cancer, any one or combination of these techniques may be employed. For instance, the first line treatment for meningiomas is surgery but may be coupled with chemotherapy in an attempt to improve survival time. Intracranial tumors (such as glioblastoma) more commonly rely on radiation therapy as surgical access to the tumor may be prohibitively dangerous.  Palliative care tends to include corticosteroids to help reduce swelling and edema around tumors as well as anti-convulsant medications to control seizures.
Prognosis of a brain tumor
Unfortunately, the prognosis varies depending on whether medical management, surgical management, or RT is chosen. The prognosis also varies with what “type” of brain tumor it is; however, it is often difficult to determine the exact “type” until surgery occurs (and a piece of tissue can be biopsied or analyzed). Some brain tumors such as meningiomas have a much better prognosis with brain surgery (to remove or debulk the tumor). Fast, invasive types of brain tumors such as glioma or glioblastoma have a poor prognosis, even in human medicine.
When in doubt, talk to your veterinarian and an oncologist or neurologist. Remember that making an appointment with an oncologist or neurologist doesn't commit you to a several thousand-dollar RT or surgical plan – it lets you weigh your options with those who have the cutting edge knowledge in that area.
Questions to ask your veterinarian
The most common indication of a brain tumor in dogs is seizure , especially seizures that begin for the first time in a dog older than five years of age. Other signs suggestive of a brain tumor include abnormal behavior (., increased aggression), altered consciousness, hypersensitivity to pain or touch in the neck area, vision problems, propulsive circling motions, uncoordinated movement, and a “drunken,” unsteady gait . Non-specific signs such as inappetance, lethargy , and inappropriate urination may also be seen.