Veteran US Republican Senator John McCain has been diagnosed with brain cancer and is reviewing treatment options, according to his office.
The options may include chemotherapy and radiation, his doctors said. The 80-year-old politician is in "good spirits" recovering at home.
The tumour was discovered during a surgery to remove a blood clot from above his left eye last week.
A Vietnam veteran, Mr McCain spent more than five years as a prisoner of war.
The six-term senator and 2008 Republican presidential candidate underwent surgery at a clinic in Phoenix, in the state of Arizona, last Friday.
Tissue analysis revealed that a primary brain tumour known as a glioblastoma was associated with the clot, a statement from the Mayo Clinic said.
"The senator’s doctors say he is recovering from his surgery ’amazingly well’ and his underlying health is excellent," it added.
"Treatment options may include a combination of chemotherapy and radiation."
Glioblastoma is a particularly aggressive brain tumour, and increases in frequency with age, affecting more men than women.
President Donald Trump said Mr McCain has "always been a fighter" and, in a statement, said: "Get well soon".