Arizona Sen. John McCain has been diagnosed with brain cancer, his hospital said in a statement Wednesday.

The former Navy officer underwent a procedure to remove a blood clot last week at the Mayo Clinic in Phoenix and more studies have revealed that McCain has a malignant tumor known as a glioblastoma.

“The senator and his family are reviewing further treatment options,” the statement read. “Treatment options may include a combination of chemotherapy and radiation.”

Glioblastomas are described as highly malignant, according to the American Brain Tumor Association.

McCain’s daughter posted a heartfelt statement on Twitter calling her father “the toughest person I know.”

“He is meeting this challenge as he has every other,” Meghan McCain wrote.

“Cancer may afflict him in many ways: but it will not make him surrender. Nothing ever has.”

The hospital added that McCain is recovering from his surgery “amazingly well.”