On Saturday, Joseph “Beau” Biden, the son of Vice President Joe Biden and former attorney general of Delaware, died after a long battle against brain cancer. Known for his sound character, military service, and political reforms, his passing came as a shock nationwide.

The most recent neurologic issue in the Biden family, Beau’s was not the first. The tragic 1972 car accident that killed his mother and younger sister left Hunter (his brother) with a skull fracture and severe traumatic brain injuries. In 1988, his dad underwent emergency surgery for a potentially deadly intracranial aneurysm.

Beau’s brain condition would turn out to be the worst of all. A Democratic superstar with a calm demeanor and passionate advocacy, the 46-year-old’s death raises new questions about the disease that killed him—one that’s alarmingly common in adults and chronically misunderstood by the public.

Brain cancer, a general term used by doctors to encompass a variety of malignant and benign tumors that grow in and around the brain, impacts thousands of people each year in the United States. This past year there were nearly 70,000 new cases and 14,000 deaths from this disease. While not as prevalent as stroke-related deaths—which claimed more than 130,000 lives in the United States this past year—these numbers are significant.

Although the term “brain cancer” is often used casually, there are many different types that occur in adults—each with a unique set of features. It may be a primary tumor, which arises from the cells that actually compose the brain itself. It could be a tumor of the skull or covering of the brain, or even metastatic disease, which occurs when a cancer from elsewhere in the body spreads into the central nervous system. Each types carries with it a separate prognosis—ranging from a life expectancy of eight months to non-life threatening.

It’s still unclear which specific type of tumor that Biden suffered from, but whether malignant or benign, it’s clear that the treatment to keep it from coming back ultimately failed. Most often, cases like Beau’s turn out to be a primary brain tumor in adults known as glioblastoma multiforme.

Glioblastoma is an aggressive and often fatal tumor, with an estimated 2-year survival rate of around 17 percent for patients between 40 and 65 years old. The underlying cause of GBM is unknown but is thought to be a disease that arises from astrocytes, the support cells of the brain, and is typically found in the cerebral hemispheres. Most cases of GBM arise directly from mutations in healthy cells. However, a small number may transform into GBM from a previously existing lower grade tumor.

Our knowledge of risk factors associated with the development of GBM is not as clear-cut as some other well-known associations, such as smoking and lung cancer. Some believe that environmental risk factors, such as radiation from cellphone use, may contribute to brain cancer—a claim that is not currently backed by science.

Unfortunately, this isn’t the first time in recent years that Washington has been affected by brain cancer. Just a short time ago, in May of 2008, former senator Edward “Ted” Kennedy passed away from an unspecified malignant glioma of the parietal lobe. A malignant glioma can often progress into a glioblastoma, which evades all the therapy we throw at it.

Treatment options typically include a combination of radiation, chemotherapy, and surgery. The goal of surgery is usually to reduce the tumor burden, followed by radiation therapy and certain chemotherapeutics. Chemotherapy may delay the disease course in some cases, but most chemotherapeutic agents for GBM have an extremely low response rate, around 10 percent. The prognosis is not particularly good for any age group, but is worse for the elderly.

Brain cancer is a deadly disease process that is alarmingly common among adults. The most common primary malignancy in adults, glioblastoma, is also one of the hardest to treat. However, there is a significant amount of research being directed at this disease. Our understanding of the underlying disease process, as well as treatment options, continues to improve, with scientists testing everything from vaccines to modified scorpion venom toxic to light up brain tumors in the operating room. Going forward, these continued advancements will enable us to improve outcomes and give hope to patients that, like Biden, receive the devastating diagnosis of brain cancer.