US Senator John McCain has been diagnosed with an aggressive form of brain cancer, glioblastoma, which also killed the late senator Ted Kennedy and Beau Biden, the son of former vice president Joe Biden.
Glioblastomas are the most common and deadliest type of brain tumor. They are part of a group of tumors referred to as gliomas.
About 12,400 new cases are expected this year, according to the American Brain Tumor Association.
"Because these tumors come from normal brain cells, it is easy for them to invade and live within normal brain tissue," it says on its website.
The tumor takes hold in star-shaped cells known as astrocytes, which make up the "glue-like," or supportive tissue of the brain.
These cells multiply fast and are fed by a large network of blood vessels.
It is unknown what causes these tumors, which may arise in the brain or spinal cord.
Their quick pace of growth can create increased pressure in the brain, and lead to symptoms like headache, nausea, vomiting, and drowsiness.
Other symptoms may include weakness on one side of the body, problems with memory, difficulties with speech and visual changes.
The cancer tends to strike most often in people over 60, although Beau Biden was diagnosed in his 40s. He died in 2015 at the age of 46.
Ted Kennedy died in 2009 at age 77, 15 months after he was diagnosed.
The median life expectancy in adults diagnosed with glioblastoma is 14.6 months.
About 30 percent of patients live for two years.
Only about four percent live for five years or longer.
The outlook tends to be poorer for elderly people, who have a median survival rate of nine to 12 months.
Treatment typically includes surgery to remove as much of the tumor as possible, followed by radiation and chemotherapy.
Around 95 percent of patients opt for surgery.
But surgery is complicated because the tumors have finger-like tentacles, and may reach into crucial parts of the brain associated with memory and language.
If doctors determine the tumor is inoperable, they may administer radiation and/or chemotherapy to slow its growth.
Drugs include temozolomide, a type of chemotherapy approved by the US Food and Drug Administration in 2005 for treatment of adult patients with newly-diagnosed glioblastoma.
Another is Avastin (bevacizumab), a targeted chemotherapy which was FDA-approved in 2009 for treatment of patients with recurrent glioblastoma and prior treatment. Avastin is also used against other forms of cancer, including colon, lung, cervical and kidney tumors.
"After radiation treatment is completed, the patient receives full chemotherapy for up to a year along with MRI scans every two to three months," said John Abrahams, chief of neurosurgery at Northern Westchester Hospital.
Clinical trials into other types of therapy are ongoing.
Experimental approaches include immunotherapy, gene and viral therapy, cancer stem cell therapy, and targeted therapy, according to the National Brain Tumor Society.