Ben Andrews was lying inside an MRI machine Thursday morning, eyes closed, praying this wouldn't be the day the tumor finally came roaring back.

That's about the only thing Andrews is guaranteed: Someday — A month from now? Three years from now? — the brain cancer will return.

With glioblastoma, it's not usually a question of if, but when.

"Please, Jesus," the 38-year-old father prayed over and over as the magnetic imaging machine beeped and hummed. "Not today."

On his way to his appointment at Memorial Hermann Mischer Neuroscience Institute, Andrews had heard the news that Sen. John McCain was diagnosed with the same disease he has been battling now for nearly two years.

Andrews knew from experience what that meant: The senator from Arizona had just learned he may not have long to live.

***

The disease revealed itself on the morning of Sept. 5, 2015.

Andrews, a nurse at Memorial Hermann Heart & Vascular Institute, had awoken with a pounding headache. He popped some Tylenol and headed into work.

He was walking through a hospital corridor when he suddenly felt incredible pressure in his head, almost as if someone had placed a hand on his forehead and shoved him back. The walls seemed to spin, forcing him to sit down.

After a few minutes the dizziness faded, and he got back on his feet.

Andrews walked over to a group of coworkers, but couldn't remember some of their names. He read the name of a long-time colleague on an assignment board but didn't recognize it. "Who's that?" he asked a friend.

Then he felt dizzy again.

Andrews thought maybe he should head home and get some rest.

A fellow nurse stopped him:

"Dude, we need to get you down to the ER."

***

Hours later, Andrews was staring at a blurry white blob on an MRI scan, trying to make sense of what the doctor was telling him. The tumor in his head was about two inches wide and lodged in his temporal lobe, a section of the brain responsible for speech and memory association.

At that point, all the doctors could tell him for sure was that the thing needed to go. They would not know for sure whether it was cancerous until after it had been removed.

RELATED: A mother's quest leads to a Houston neurosurgeon and one of the hardest decisions of her life

Days later, Andrews underwent what's known as an awake craniotomy, a neurosurgical technique in which a patient is revived while the brain is being operated on.

With Andrews awake, Dr. Nitin Tandon, the UTHealth neurosurgeon, was able to ask him questions while activating specific sections of the brain, giving him a better understanding of which tissue was safe to remove.

It's a balancing act, Tandon explained, between removing as much of the tumor as possible while stopping short of damaging the brain.

After he cut out as much as he could, the surgeon placed a piece of the tumor into a dish and sent it off to be tested.

***

"What does this mean?" Andrews remembers asking two weeks later when the results came back. "Am I going to die?"

The neuro-oncologist, Dr. Jay-Jiguang Zhu, didn't sugar coat things: Glioblastoma is an extremely aggressive and incurable brain cancer, he told him. They would do everything they could to keep it from spreading, but there is no way to ever get rid of it.

Andrews had not heard of the disease; he soon wished he never had.

Each year in the U.S., about 12,000 people are diagnosed with glioblastoma tumors. About 70 percent die within two years, others within just a few months. Some patients make it longer. Three years. Five years, if they're lucky. In rare cases, some people — often younger patients like Andrews — have survived more than a decade with the disease.

Inevitably, though, glioblastoma comes back. The problem, Zhu said, is that surgery cannot completely eliminate the tumors, which have microscopic, tentacle-like tendrils that extend deep into the brain.

After surgery, patients undergo months of radiation and chemotherapy treatments to eliminate as much of the cancer as possible.

Then, they wait.

***

What do you do when you've been delivered a diagnosis that sounds a lot like a death sentence?

Some patients quit their jobs. Get in touch with old friends. Start to get their affairs in order. Withdraw from society.

Andrews considered going that route. Then he thought about his two young kids. His parents. His girlfriend, Brittany, who had supported him throughout the ordeal.

"I decided I just didn't want this thing to change my life," Andrews said.

He continued training for a marathon while undergoing radiation treatments. He kept showing up for classes to get his master's degree as a nurse practitioner. He returned to his job as a nurse at Memorial Hermann and even spent some time interning with Zhu, where he helped comfort and care for patients newly diagnosed with glioblastoma.

JOHN MCCAIN'S BRAIN CANCER: The medical lowdown on glioblastoma

"He's incredible," said Zhu, an associate professor in the department of neurosurgery at UTHealth's McGovern School of Medicine. "It's inspiring how he's approached this and stayed positive. Most people struggle to do that."

Based on his public remarks since his diagnosis was announced this week, McCain seems to be taking a similar approach. On Twitter Thursday, he thanked everyone for the outpouring of support. And he had a message for his "sparring partners" in the Senate:

"I'll be back soon," he wrote, "so stand-by!"

I greatly appreciate the outpouring of support - unfortunately for my sparring partners in Congress, I'll be back soon, so stand-by! — John McCain (@SenJohnMcCain) July 20, 2017

***

Andrews tries not to obsess over how much time he has left, he said. He's focused instead on making the most of each day.

Once every two months, though, when he goes in for his regular MRI check-up, he's reminded that he's one bad screening from losing it all.

So far, the cancer hadn't spread since the surgery nearly two years ago, which means Andrews already has outlived the average glioblastoma patient. Sometimes he thinks, hopefully, that maybe it won't ever come back.

Maybe he'll be the anomaly.

As he awaited the results of his latest scan Thursday, though, the familiar feeling of dread washed over him. What if this was the day?

Andrews was relieved an hour later when he sat down with Zhu to go over the results.

The doctor had good news for him — at least for today.

"That's all I can ask for," Andrews said afterward. "I'm thankful for every day I get."