But incredibly, Mike took the cancer -- what many would consider an formidable obstacle -- and turned it into a challenge. "You look at yourself in the mirror when you're 23 years old, and you see yourself going bald and overweight. You change as a person. It's either, you sit on the couch and watch life go by, or you actually get out and do cool things," says Mike.
And so the brothers made a pact and promised each other that if Mike survived the cancer they'd do something big together, something adventurous. "Ultimately you ask yourself, what the heck am I doing here? And I am really living?" asked Sean.
When Mike went into remission after four months of chemotherapy, they planned their trip to Pamplona.
The Lenahans were lucky, as their wounds were largely superficial, and they escaped any permanent disability.
"There's scar tissue," says Mike. "I can't believe I'm running again so soon, just like nothing ever happened."
Both of these traumatic events have helped to galvanize the bond between the brothers. "I feel like we got closer through that experience," says Sean. "It's nice to know that when something really bad goes down, both of us immediately found one another without really thinking about it. That's a strong connection."
And in case you're wondering, they'd do it all over again in a heartbeat. "I'd like to finish that race," says Sean. And Mike? "For sure."