Sen. John McCain (R-Ariz.) has been diagnosed with a brain tumor, his office said Wednesday, throwing into doubt when and if he will return to Washington to resume his duties in the Senate.

The Mayo Clinic said doctors diagnosed a tumor called a glioblastoma after surgery to remove a blood clot above McCain’s left eye last week. The senator and his family are considering treatment options, including a combination of chemotherapy and radiation, according to the hospital.

McCain, 80, has been away from the Senate this week, recovering from the surgery and undergoing tests. His office issued a statement describing him “in good spirits” and noting that his doctors say his underlying health is excellent — but not indicating when he will return to the Senate.

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