TEHRAN, Young Journalists Club (YJC) - The 80-year-old Arizona lawmaker’s office made the announcement on Wednesday, quoting a statement by the Mayo Clinic, whose doctors performed the surgery in Phoenix last week.
According to the statement, tests had "revealed that a primary brain tumor known as a glioblastoma was associated with the blood clot."
"The senator and his family are reviewing further treatment options," the statement added, noting they may include a combination of chemotherapy and radiation.
Glioblastoma is a particularly aggressive brain tumor affecting adults. It is of the same category of cancer that led to the death of another icon of the US Senate, Ted Kennedy, who died in 2009 at age 77.
This is not McCain's first bout with cancer. Doctors removed several malignant melanomas on McCain's skin in the 1990s and 2000s, including an invasive melanoma in 2000.
Experts had said this week that McCain's latest operation suggested the possibility of a return of cancer.
McCain's office said the senator "is in good spirits as he continues to recover at home with his family in Arizona," and that he will consult with his care team about when he might be able to return to work in Washington.
The news triggered a flood of messages of support from across the political spectrum for McCain, who chairs the Senate Armed Services Committee and is in his sixth term in the upper chamber of Congress, Presstv reported.
"Senator John McCain has always been a fighter. Melania and I send our thoughts and prayers to Senator McCain, Cindy, and their entire family," President Donald Trump said in a statement. "Get well soon."
Trump had been at odds with McCain, one of his main critics before and after last year’s presidential election. The new Republican president had once mocked McCain for being captured in the Vietnam War.
Barack Obama, Trump’s predecessor, also expressed support for McCain.
"Cancer doesn't know what it's up against. Give it hell, John," the former president tweeted.