WASHINGTON — Arizona Sen. John McCain has been diagnosed with a brain tumor after doctors removed a blood clot above his left eye last week, his office said in a statement Wednesday.The 80-year-old Republican has glioblastoma, an aggressive cancer, according to doctors at the Mayo Clinic in Phoenix. The senator and his family are reviewing further treatment, including a combination of chemotherapy and radiation."On Friday, July 14, Sen. John McCain underwent a procedure to remove a blood clot from above his left eye at Mayo Clinic Hospital in Phoenix. Subsequent tissue pathology revealed that a primary brain tumor known as a glioblastoma was associated with the blood clot," his office said in a statement.About 20,000 people in the U.S. each year are diagnosed with a glioblastoma, a particularly aggressive type of brain tumor.