His doctor first diagnosed it as a pinched nerve. Daniel Jacobs thought the pain running down his leg might be sciatica.
''We were both wrong,'' Jacobs said.
It was on a USO tour of the Middle East when the boxer first felt numbness in his leg. He ignored it at first, thinking it would go away.
But by the time he headed home, Jacobs was using a cane to walk. Three weeks later, he was in a wheelchair.
An MRI showed a tumor on his spine. A biopsy showed it to be malignant.
Hard to imagine that just weeks earlier Jacobs had entered a ring in California full of energy and in the best shape of his life. It was short work, with Jacobs knocking his guy out in the first round to continue a comeback from the only loss of his pro career.
Now he was in the fight of his life, facing a foe he didn't totally understand.
''By that point in my mind boxing was furthest thing to think about,'' Jacobs said. ''My life was No. 1 and having a life for my family and getting better so I could be a father to my son.''
Doctors who removed the tumor said he would never fight again. It was too close to his spine, and the spine is in play with almost every punch a fighter takes.
But Saturday night he'll go into the ring to defend his piece of the middleweight title against veteran Sergio Mora. He'll do it on national television from Barclay's Center in his hometown of Brooklyn.
After beating cancer, he's not too concerned about anything he'll face in the ring.
''It wasn't for the faint of heart,'' Jacobs said of a fight that cost him the better part of two years in the prime of his career. ''You've got to be a champion inside your heart and mind to be able to conquer something like that. It just proves I can jump over any hurdle, any obstacle.''
If that's not a mindset Jacobs was born with, it's one he has embraced ever since an encounter with a bully led him to a boxing gym for the first time when he was in eighth grade. He learned enough to beat the bully in a fight a few weeks later, but what he learned most was that he had found his true calling.
''Little did I know I'd fall in love with it the very second I walked in the PAL gym,'' the 28-year-old said. ''There was just something about the smell of the gym, the sweaty boxing gloves, the ropes and the heavy bag. I felt like I was at home.''
Jacobs would become a top amateur, winning national titles in the Golden Gloves and becoming the AAU middleweight champion in 2006. He turned pro the next year, knocking his first opponent out in just 29 seconds on the undercard of the Floyd Mayweather Jr.-Ricky Hatton fight in Las Vegas.
Jacobs won his first 20 fights before being stopped in the fifth round of his 2010 bout with Dmitry Pirog. The loss was devastating, but Jacobs came back to win his next two fights within the distance.
Then the tumor was discovered, and Jacobs began a battle of another sort. Meanwhile, the bills mounted and he didn't know if he would ever be able to make a living in the ring again.
''I went from being a world-class athlete to having to move back in with my mom because of all the bills stacked high,'' he said. ''You don't know how you're going to provide for yourself in the near future.''
Jacobs finally began training again after his last radiation treatments. For months he labored in the gym, hoping against hope he would find what he once had.
''I always said to myself that if I wasn't 100 percent ready in the gym I wouldn't risk my life inside a boxing ring,'' he said. ''But one day I started sparring and it started to feel like things were getting better. I started to get my touch back, my pivots and old moves like I used to do.''
The real test, though, came in his first fight back. It came on the first boxing card at the new Barclay's Center, and Jacobs passed it by knocking out Josh Luteran in the first round.
Jacobs would go on to win the WBA version of the 160-pound title, though he is still not the first name people talk about in the middleweight division. That could change, however, if he gets - and wins - fights against the likes of Miguel Cotto, Canelo Alvarez and Gennady Golovkin.
''That's the way the sport goes,'' Jacobs said. ''You're not a name unless you beat a name. But I'm looking forward to stepping up in competition and creating a name for myself.''
Whether that happens depends on a lot of things going right in a sport where things can go bad quickly.
But after beating cancer, it hardly seems like an even fight.
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Tim Dahlberg is a national sports columnist for The Associated Press. Write to him at tdahlberg(at)ap.org or http://twitter.com/timdahlberg
