In a brief statement, the senator's office provided an assessment from Mark Gilbert, chief of neuro-oncology at the National Institutes of Health's National Cancer Institute.
President Trump told reporter's on Sunday that he spoke to McCain's wife, Cindy, and wished the couple well.
"Thank you to everyone for their kind words", she wrote.
In July, the 81-year-old senior senator from Arizona was diagnosed with glioblastoma, an aggressive form of brain cancer. "I wish John well", he said.
"They've headed back, but I understand he'll come if we ever needed his vote, which hopefully we won't", Trump said after returning to the White House from Camp David.
President Donald Trump says Republican Sen. If just two Republican senators vote against the bill, it will die on the floor of the Senate. Top U.S. Republicans said on Sunday they expected Congress to pass the tax bill.
On Wednesday his office released a statement saying he is receiving treatment at Walter Reed Medical Center for "normal side effects" of his ongoing cancer treatment.
McCain, who left Washington Sunday, will spend the holidays with his family. "My father is doing well and we are all looking forward to spending Christmas together in Arizona". The bill has already passed the House of Representatives and Senate, but differences in each version needed to be reconciled before a final vote could take place.
This week, the GOP will try to pass a sweeping $1.5 trillion tax package in the Senate with a razor-thin majority and all Democrats opposed to the legislation. Marco Rubio (R-FL) and Bob Corker (R-TN) announced their support for the bill after winning some amendments or provisions.
McCain rebounded quickly, but his condition has appeared to worsen in recent weeks.
'The truth is that, as anyone knows whose family has battled cancer or any significant disease, that oftentimes there are side effects to treatment that you have, ' Domenech explained when talking about McCain's ailment today.