Sen. John McCain headed home to Arizona on Sunday after being briefly hospitalized for a viral infection. The Arizona senator's return home means he will miss out on the tax reform vote scheduled for this week.

On Sunday, his office released a joint statement with his doctors, explaining why he was hospitalized last week.

Dr. Mark Gilbert, Chief of Neuro-Oncology at the National Institutes of Health's (NIH) National Cancer Institute, said McCain 'has responded well to treatment he received at Walter Reed Medical Center for a viral infection and continues to improve. An evaluation of his underlying cancer shows he is responding positively to ongoing treatment.'

Cancer patients like Sen. McCain are more susceptible to viral infections because their immune system is weakened during treatments like chemotherapy.

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Sen. John McCain will miss votes this week on the tax package, as he headed back to Arizona today

Sen. John McCain's son-in-law Ben Domenech appeared on Face the Nation and told viewers he was in 'good spirits' and 'doing well'

McCain's new son-in-law, Ben Domenech, also gave an update on the senator's condition on Face the Nation on Sunday.

'Well, John, I'm happy to say that he's doing well,' Domenech answered Face the Nation host John Dickerson, who had asked about the Republican lawmaker. 'He's in good spirits. And he's looking forward to heading back home in Arizona for the holidays.'

McCain's daughter Meghan herself has since tweeted thanking everyone for their support and assuring that her father is recovering.

'Thank you to everyone for their kind words. My father is doing well and we are all looking forward to spending Christmas together in Arizona. If you’re feeling charitable this Christmas @HeadfortheCure or @NBTStweets to help find a cure for brain cancer is what I recommend.'

CBS News later reported that McCain is heading directly to Arizona and miss key votes on the Republican tax package, which will take place next week.

McCain's absence shouldn't derail the package, despite the slim GOP majority in the Senate, as Sens. Bob Corker, a Tennessee Republican, and Marco Rubio, a Florida Republican, have said they would vote in favor of the bill after, at first, suggesting they wouldn't.

McCain was admitted to Walter Reed Hospital on Wednesday due to the 'normal side effects' of his cancer treatments,' his office said.

'As ever, he remains grateful to his physicians for their excellent care, and his friends and supporters for their encouragement and good wishes,' the statement said.

Domenech married Sen. John McCain's (left) 33-year-old daughter Meghan (right) in November. She tweeted some suggestions for brain cancer charities Americans could donate to as she thanked people for their 'kind words' about her dad

In July, the 81-year-old senior senator from Arizona was diagnosed with glioblastoma, an aggressive form of brain cancer.

More recently, McCain tore the Achilles tendon on his right foot, which forced him to wear a walking brace and then use a wheelchair in order to get around the U.S. Capitol.

CBS noted that some of the symptoms of glioblastoma include headache, general malaise, along with vision and speech problems.

'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. 'The senator's been through a round of chemo and he went – and was hospitalized this week at Walter Reed.'

Domenech, who married Meghan, McCain's 33-year-old daughter in late November in Arizona, said his father-in-law was looking forward to spending the holidays in the Grand Canyon state.

As of late, Sen. John McCain has had to use a wheelchair to get around Capitol Hill after injuring his Achilles heal and being treated for cancer

'Our thanks to everyone who has been sending thoughts and prayers to the senator this week,' Domenech said. 'We greatly appreciate it. And he remains one of the toughest men on the face of the earth, as you know.'

Meghan McCain also chimed in, tweeting Sunday afternoon on Twitter about her dad.

'Thank you to everyone for their kind words,' she wrote. 'My father is doing well and we are all looking forward to spending Christmas together in Arizona.

'If you’re feeling charitable this Christmas @HeadForTheCure or @NBTStweets to help find a cure for brain cancer is what I recommend,' she said.