Republican Sen. John McCain has been treated at a military hospital for a viral infection and is "responding positively" to ongoing treatment for brain cancer.

That's the word Sunday from Dr. Mark Gilbert, chief of Neuro-Oncology at the National Institutes of Health's National Cancer Institute. The senator's office released a statement with the doctor's assessment.

His office says McCain has returned to Arizona and will undergo physical therapy and rehabilitation at the Mayo Clinic in the state. The statement says the senator appreciates the outpouring of support from people around the country. His office says the 81-year-old senator "looks forward to returning to Washington in January."

McCain will miss the vote this week on the tax bill. The GOP is likely to have enough Republicans to pass the measure.