When Senator John McCain was diagnosed with glioblastoma in July 2017, few Americans had heard of the condition. But glioblastoma (also called glioblastoma multiforme, or GBM), affects tens of thousands of people. Each year, approximately 14,000 Americans are diagnosed with this particularly aggressive form of brain cancer. Most, like McCain at his diagnosis, are active, otherwise healthy people. Here are six facts to help you understand glioblastoma: 1. Glioblastoma is the most common form of brain cancer in adults. Approximately 35 to 40% of all cancerous brain tumors in adults are glioblastoma. (Just 3% of childhood brain tumors are glioblastoma.) This kind of cancer starts in star-shaped brain cells called astrocytes. Unfortunately, these cells are spread throughout the brain and supported by a broad network of blood vessels, so the cancer can grow quickly. 2. Seizures can be a symptom of glioblastoma. About half of all people with brain tumors will eventually have a seizure. (Of course, not all seizures are due to brain tumors.) Other symptoms of glioblastoma include headache, nausea, vomiting, drowsiness, weakness or difficulty with movement, memory problems, visual changes, and speech disturbances. Symptoms will vary depending on the size and location of brain tumors, and may worsen over time as the cancer grows and increases pressure in the brain. 3. Glioblastoma is difficult to treat. Glioblastoma presents some unique challenges. One: brain tumors contain a lot of different kinds of cells. Certain treatments may be effective against some cells, while other cells thrive. It’s also exceedingly difficult to get treatment to the brain, because the body’s blood-brain barrier–designed to protect the brain from harmful substances–drastically limits what gets into the brain. Glioblastoma is much more difficult to treat than breast, colon or prostate cancer. 4. Glioblastoma survival rates are increasing. For adults ages 55 to 64, the five-year glioblastoma survival rate, or the likelihood of being alive five years after being diagnosed with glioblastoma, is just 4%. But progress is being made. In the mid-1990s, the average length of survival after diagnosis was 8 to 10 months; today, it’s 15 to 18 months. Less than a generation ago, almost no one with glioblastoma survived five years; now, the overall five-year survival rate for glioblastoma is 15%. 5. Surgery can help relieve symptoms. Surgery won’t cure glioblastoma, but it can help patients feel better and slow the growth of cancer. During surgery, physicians remove as much of the brain cancer as possible; they can also relieve pressure in the brain, which may result in decreased symptoms. (Most common glioblastoma symptoms, such as headaches, nausea, and visual changes, are caused by pressure in the brain.) Many patients with glioblastoma also undergo chemotherapy and radiation. Doctors use these treatments to slow the spread of cancer and control symptoms. 6. Vaccines may be used in the future to treat glioblastoma. Scientists are constantly studying new treatments for glioblastoma. One possible treatment currently under investigation is dendritic cell vaccines, or vaccines made up of patients’ immune cells that are engineered to target proteins produced by glioblastoma cells (but not normal brain cells). Other promising treatments include CAR T-cell therapy (a type of immunotherapy that’s worked in some patients with melanoma and leukemia) and combination therapy, which use multiple treatments at the same time (or in sequence) to treat cancer. Each of these treatments is first tested via clinical trials. Your doctor can help you figure out if you or your loved one might be eligible for a glioblastoma clinical trial.