CHICAGO — A variety of malignant brain and central nervous system tumors kill about 15,000 people in the United States each year, often after difficult courses of surgery, radiation and chemotherapy, according to experts and data from various cancer organizations.

Officials have not disclosed the type of brain cancer that killed Vice President Biden's son Joseph Robinette "Beau" Biden III at age 46 on Saturday night. But assuming he suffered from a primary cancer — not one that spread from another part of the body — the most likely is a glioblastoma, an aggressive cancer of the brain's supportive tissue, two experts said.

Patients with Grade 4 glioblastomas — the most aggressive type survive a median of 14.6 months after diagnosis, said Brian Alexander, a radiation oncologist at the Dana-Farber Cancer Institute in Boston. But adults can suffer from Grade 2, 3 or 4 malignancies, living for 10 years or more if they have the mildest type, and younger adults like Biden tend to live longer than older ones, Alexander said.

Former Massachusetts senator Edward M. Kennedy died in August 2009, 15 months after he suffered a seizure and was diagnosed with a malignant glioma, the most common form of brain cancer. A glioblastoma is a sub-type of glioma.

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Brain cancers also "can morph from a lower-grade version to a higher-grade version over time," said Deepa Subramaniam, director of the brain tumor center at Georgetown Lombardi Comprehensive Cancer Center.

Beau Biden was first diagnosed in August 2013 and after surgery, radiation and chemotherapy returned to normal duties in November that year. But his cancer recurred this spring, and he began treatment again at Walter Reed National Military Medical Center.

In 1988, Vice President Biden, then a senator from Delaware, underwent two brain surgeries himself for a cranial aneurysm, an enlargement or bulge in a blood vessel caused by a weakness in its wall.

Nearly 23,000 adults, more of them men than women, will be diagnosed with primary brain cancers this year, according to Cancer.net, a web site of the American Society of Clinical Oncology, whose members are gathered here for their annual conference.

Brain tumors are a particularly common form of cancer in children. About 4,300 children and teens will be diagnosed with malignant tumors this year, more than half of them younger than 15.

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Unlike most other cancers, brain tumors generally do not spread to other parts of the body. They kill by interfering with normal body function, depending on their location in the brain. Malignancies can develop in most areas of the brain, Alexander said.

Treatment generally involves surgery first, if possible, to remove as much of the tumor as possible, Alexander and Subramanian said. Surgeons sometimes will leave portions of the tumor in the brain to preserve body function, Alexander said.

Surgery is followed by radiation and chemotherapy, often with the drug temozolomide, which patients tend to tolerate well, Subramanian said.

"For most incurable brain tumors, the primary challenge is managing the portions of the tumor that are undetectable by diagnostic imaging," said Nader Sanai, a brain tumor surgeon and brain cancer researcher at Barrow Neurological Institute in Phoenix. "These tumor cells are often the source of recurrence, traveling undetected to other brain regions of the patient and then driving the formation of new areas of growth with little warning." Most malignant brain tumors eventually recur, Sanai said.

Oncologists are learning more about the genetics of brain tumors, but that hasn't yet yielded any transformative therapies, Alexander said. Still, "the more we learn about the biology of [such cancers], the better we get at being able to tell how well a person might do," Subramaniam said.

With brain tumors, a variety of complications can appear, said Eric T. Wong, a neuro-oncologist at Beth Israel Deaconess Medical Center. The patient can develop seizures. Radiation can also induce cognitive changes, such as short-term memory problems, or problems processing information in a timely fashion. Patients can also develop infections, clots in their legs and lungs, and sleep problems.

“There’s a litany of complications associated with having the tumor as well as secondary ones related to the treatment,” he said. “And there’s less government-funded research dollars going into brain cancer research and cancer research in general.”

Brady Dennis and Lena H. Sun contributed to this report.

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