John McCain’s son says senator ‘sounds better than the day before’

"I talk to him about once a day on the phone, and every time I talk to him he sounds better than the day before," Jack McCain told the Arizona Republic.

"He is a very strong human being with the type of will that I have not seen paralleled anywhere else, and I have no doubts that he's going to be fine."

In July, John McCain, R-Ariz., shocked the nation when he revealed that, at 80 years old, he had been diagnosed with brain cancer.

The cancer, glioblastoma, was discovered during cranial surgery to remove a blood clot above his left eye. It is a typically malignant and aggressive cancer, with a median survival rate of 14.6 months.

"The diagnosis he has is not a good one. But of all of the things that have happened in this man's life, of all of the times that his life could have ended in the ways it could have ended, this is by far one of the least threats to him and that's kind of how he views it," Jack McCain said.

"He's very sober about it. He understands the implication and the weight of it. But for not one minute has he let that take over his feelings towards how hard he has to fight."

Jack McCain, 31, is a Navy lieutenant and helicopter pilot. He is the fifth of John McCain's seven children, but the oldest son of John's current marriage with Cindy McCain.

McCain's office has not provided an official update on the senator's health since Dec. 17, when they said he would return to the Senate in January, a goal he probably will miss.

Although John McCain, now 81, has faced setbacks including injuring his Achilles heel last fall because of steroids he is taking in treatment, Jack McCain said he believes his father will overcome.

"He is more than double my age and can outpace me in almost everything," the younger McCain said. "I have absolutely zero doubt that this is something he can not only beat but conquer."