As you’ve no doubt heard, veteran U.S. Senator John McCain was just diagnosed with a brain tumor, and many people are wondering about the prognosis and survival rate of this type of cancer. McCain joins other high-profile individuals who’ve also had brain tumors, including Senator Ted Kennedy and former vice president Joe Biden’s son Beau.

McCain has a type of tumor called a glioma, which arises from cells called glia, explains Dr. Andrew Chi, chief of neuro-oncology at Perlmutter Cancer Center at NYU Langone Medical Center. Glia are support cells in the brain and spinal cord. Glioblastoma multiforme, as it’s technically called, is a fast-growing, advanced cancer and the most common of the gliomas. Approximately 56 percent of all adult brain tumors are glioblastomas; these also occur in children. Some low-grade glioblastomas are precancerous, but about 70 percent of them eventually become malignant.

Chi says glioblastomas typically don’t spread outside the brain, although they do spread in the brain, making them very difficult to diagnose and treat. “The classic presentation [of a brain tumor] is a neurological event [such as a seizure],” says Dr. Vinay Puduvalli, an oncologist at The Ohio State University Comprehensive Cancer Center. This neurological event triggers a CT scan to determine what’s going on.

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The symptoms of a brain tumor vary depending on what part of the brain the tumor is affecting. For example, the tumor could affect a patient’s vision, hearing, speech, balance or mood and personality. Morning headaches, memory problems, seizures and numbness or tingling in the limbs could also be signs of a brain tumor. As these tumors grow and spread, they can cause pain and increasingly severe symptoms.

Because so many other types of cancer spread to the brain, tumors in the brain are common. In fact, Puduvalli says, more than 250,000 patients are diagnosed with brain metastases each year. However, primary brain tumors, such as glioblastomas, are not very common, occurring in about 12,000 people a year in the U.S. Unfortunately, the mortality rate is very high. Even with treatment, a patient’s average lifespan after diagnosis is roughly 15 months, which is about how long Kennedy lived after he was diagnosed. Furthermore, despite treatment, nearly 100 percent of glioblastomas recur within a year.

Unlike lung cancer, for example, which is clearly linked to smoking, there are no real identifiable environmental risk factors for glioblastoma, Chi says, other than perhaps high doses of radiation. For example, radiation therapy for another medical condition may raise your risk of developing a glioblastoma.

“The real clear risk factor is age,” Chi says. “Every decade [of life], your risk goes up.” Although McCain’s history of melanoma skin cancer is not related to his glioblastoma, Chi says it’s not unusual to see older people (McCain is 80) with two types of primary cancers, since age is a significant risk factor for all cancers. There’s also a slightly elevated risk for family members of people with glioblastomas, Chi says.

[See: 6 Things You Didn’t Know About Glioblastomas.]

Treating Brain Tumors

Brain tumors present unique treatment challenges. “A glioblastoma becomes embedded into the fabric of the brain,” Puduvalli says. “It’s so hard to treat.”

Chi echoes the sentiment. “By the time we see a tumor on an MRI or see it in the operating room, the cells have already spread,” he says. “We can’t see [them. The tumor] sends little fingers [of cancer cells] throughout the brain.”

Treating glioblastomas is a challenge for several reasons. The brain is protected by the blood-brain barrier, a layer of tightly packed cells that prevents viruses and toxins in the bloodstream from harming the brain. Some chemotherapy drugs cannot pass through the blood-brain barrier, so oncologists look for ways to temporarily open or disrupt this barrier to effectively deliver chemotherapy to tumors. Furthermore, there are consequences to treating brain cancer, Chi says. Just as the cancer itself can harm brain functioning, treatment can also impair speech, memory or movement, for example.

If the tumor is surgically accessible and the patient is a candidate for surgery, a surgeon may try to remove as much of the cancer as possible, which is called a craniotomy. Surgery is generally not curative, since the tumor cells have likely infiltrated other areas of the brain. Radiation therapy is sometimes an option. However, because glioblastomas are such aggressive cancers, it requires high doses of radiation to kill them. Radiation therapy is sometimes used along with other treatments. “For each individual person, we tailor treatment based on age, functional status and other medical conditions,” Chi says.

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New Treatments on the Horizon

Puduvalli says there have been advances in treatment for glioblastomas over the past 10 or so years. For example, clinical trial results showed that combining radiation therapy with the drug pembrolizumab increased survival in some patients. Researchers are uncovering molecular markers that help predict prognosis, as well as identifying individual genetic profiles that might respond to targeted therapies. Other potential treatments, including immunotherapy, which helps the immune system fight the cancer, are in clinical trials. “Often, tumors suppress the immune system,” Puduvalli says. “We’re learning how this works and how to uncloak it. It’s a powerful approach, using your own body to fight tumors.”

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