This man found an unusual motivation to run. Now he's heading into his 600th marathon.

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Man overcomes daunting diagnosis to run 600th marathon
Avid runner Tom Perri is preparing for a milestone marathon in North Dakota, refusing to let his stage 4 prostate cancer diagnosis define him.
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Tom Perri is about to hit a major milestone: 600 marathons.
“I started doing two marathons and three, then four, and then slowly the number just started multiplying," says 60-year-old Perri.
The avid runner from Maple Grove, Minn. averages 36 races a year but believe it or not, that's the least of Perri's achievements.
He has stage 4 prostate cancer and has continued running marathons since the diagnosis. He's also continued to help other runners reach their goals.
"I just love to help people do that stuff," said Perri. "It's all about helping another runner."
Watch how he does it in this video.