EAU CLAIRE, Wis. (WEAU) -- Running a marathon is a feat in itself, but doing it with terminal cancer is even harder to fathom.
However, that's just what a Mayo Clinic Health System physician did despite facing tongue cancer.
When talking with Dr. David Eitrheim, an avid runner and family man, his illness appears to be one of the last things on his mind.
But, since beginning his battle with cancer in July 2013, Dr. Eitrheim says he's learning lessons, many of which are life- changing.
"It's something I've always enjoyed. I ran my first marathon in 1976.
It's been something that's been part of my life for many years," he explains.
But, in July of 2013, Dr. Eitrheim received news that stopped him in his tracks.
"I would try to even run two to three miles and I found it was uncomfortable to run so I quit running and I didn't run for months."
He had tongue cancer; by May 2014 he found out it was terminal.
"I think I was at a point where I couldn't imagine living the rest of my life in pain."
He was dealing with pain in his jaw and neck, and grappling with his own mortality.
"The idea that I was approaching the end of life."
Eitrheim's friend, and Pallative Care Physician, Jim Deming says they began chemotherapy to halt the rapidly growing cancer and lessen the pain.
"There were a number of us that thought he would not be with us very long," explains Deming.
Given nine to 12 months to live, Dr. Eitrheim says the treatment began to work.
"It was Jim Deming again that said, 'What would give you a really great day?' And there was no question in my mind. It was I'd love to run another marathon."
With lessening pain from the palliative care, Eitrheim surprised his running buddies.
"I said today we're going for a run guys and we ran five miles and then next week it was ten, the next week it was 15."
Eitrheim signed up for his 90th marathon, the "Rails to Trails Marathon" in November and with support from family and friends crossed the finish line.
"It was emotional. It was just this unbelievable feeling of gratitude that I could do this again."
An inspiration, says Dr. Deming.
"I want to thank you for your fighting spirit, and your faithfulness and your humility because you've inspired us, so thank you, thank you," says Deming.
Eitrheim says he'll continue running his longest marathon, the one of life, one mile at a time.
"We have a tendency to always look tomorrow and I think one of the things I've learned having a terminal illness is live today, and live life fully."
Nine months out of his 12 month diagnosis, Eitrheim says he's spending more time with wife and two children, something he says he realizes is more important than ever.
He says he's still planning on running more marathons.
He's signed up for the Eau Claire Half- Marathon in May, as well as the Grandma's Marathon in June.