The resilience of U.S. marathoner Serena Burla

OTTAWA, ON - MAY 27: Serena Burla of the USA racing in the Ottawa 10K during the Tamarack Ottawa Race Weekend, May 27, 2017, in Ottawa, Canada. The Ottawa 10K is part of the International Amateur Athletics Federation (IAAF) 'Gold' series of international Sean Burges/Icon Sportswire

As Serena Burla pushed hard toward the finish at last summer's World Marathon Championships in London, she tried to stay in the moment. She took in the sights and sounds along the route to the finish at Tower Bridge. She embraced the cheers of fans lining the street. She paid attention to how good it felt to be strong and fast.

"I remember the last probably 1,000 meters being, 'You've just got to soak this up because you don't know what the future holds, so just appreciate every step,'" she said.

She ran as though it were her last race because she was terrified it might be.

Weeks earlier, Burla had discovered a marble-size lump on the back of her right thigh. It was in the area where a malignant tumor -- synovial sarcoma, a rare form of cancer -- and much of the surrounding muscle had been removed in 2010. "I'm definitely an optimist," she said, "but something like that, I was like, 'It's back. It's back.' I just had a feeling."

Burla ran a strong race that August day. She finished 11th in 2:29:32, the second American behind bronze medalist Amy Cragg. Coupled with her marathon personal-best of 2:26:53 in Osaka, Japan, earlier in 2017, Burla -- who had just turned 35 years old -- had one of her best years as a marathoner. But she feared what might come next.

"I really didn't know what [the doctors might] have to take out or what my overall health was or if they would have to treat it with additional steps besides surgery," said Burla, who lives in northern Virginia with her husband and son.

Just days after returning from London, Burla met with doctors at Memorial Sloan Kettering Cancer Center in New York City. They did tests that confirmed that the cancer had returned. This time, the tumor was smaller and closer to the surface. Doctors removed it without taking as much surrounding tissue as they had in her first surgery, and they'll monitor her closely.

"Fortunately, it wasn't in a whole different muscle group. It was in a very similar area, so they had already removed the muscle," Burla said.

Also, doctors decided she didn't need chemotherapy or radiation treatment. Still, it was a scare and a setback. She had to take time to recover, something her young son couldn't grasp. "I wasn't able to move around and play and drive, and he wasn't used to me moving around so slow," she said.

A little more than seven months later, Burla is running again. In January, she ran her first competitive race post-surgery, the Aramco Houston Half Marathon, finishing 15th in 1:11:41, more than a minute and a half over her 2010 PR in the distance (1:10:08), also at Houston. On March 18, she was fifth in the United Airlines NYC Half, running 1:13:15 in cold, windy conditions. On April 16, she'll start her third Boston Marathon.

"I'm experienced enough to know that a marathon is a whole different beast than a half marathon," she said. "But I was happy with those performances. I still have the heart and the passion."

That's one thing Burla's longtime coach, Isaya Okwiya, never doubted. He says Burla is as tough and resilient as anyone he's ever known. She has bounced back faster than she did after the first surgery, which he described as "incredibly radical."

Now comes Boston, in which Burla has struggled. The former University of Missouri standout has had a good career -- winning the U.S. Half Marathon title in 2013 and twice competing for the U.S. in the World Marathon Championships -- but in Boston, she had to drop out in 2013 because of the flu and in 2014, she went out too fast and finished 18th.

For once, she'd like to have a great day at Boston.

"I still want to walk away with, 'That was the Boston experience,'" she said. "I don't know what that will look like on race day -- we always want more -- but no matter what, Boston's always going to be special to me. I want to walk away with my head held high."