When Nestor Paonessa runs on trails, he is always concentrating.He looks down at his feet, making sure he doesn’t step in a rut and sprain his ankle on the uneven ground. Sometimes, his eyes watch for copperhead snakes, which he often sees slithering across the Al Buehler Trail. On really long runs, he is gauging the best time to slow to a speed-walk. But no run has demanded more of Nestor's focus than the 100-miler. In April, Nestor completed the Umstead 100 Ultra—a 100-mile endurance race through William B. Umstead Park in Raleigh. He ran it with a stage IV glioblastoma brain tumor. The race was a high point during a period of two years that have taken him back and forth from the depths of sadness and fear to the highs of hope and happiness. Now, Nestor is still fighting for his life as he receives treatment at Duke’s Preston Robert Tisch Brain Tumor Center. But he believes he can overcome anything after completing that 29-hour race.“I can and will conquer brain cancer,” he says. * * * Before Nestor, 36, was diagnosed with cancer in June 2015, life was going well. He had just returned from a hiking trip to Machu Picchu, completed a grueling ultra-marathon trail series and was preparing to move into a new house in Durham with his wife. As an assistant general manager and personal trainer at Empower Personalized Fitness, he was in the best shape of his life.But then headaches suddenly became common. His eyesight started to appear doubled and tilted. Soon after going to the eye doctor, Nestor was staring at an MRI scan that showed a golf ball-sized tumor on his brainstem, pushing up on the nerves of his eye. The median survival time for someone with that tumor—less than 15 months. Nestor's life transformed. He went into surgery days later to remove the tumor, and then started receiving radiation and began chemotherapy. He could no longer drive because of his eyesight. He could no longer work as much. Going on hikes and running—his favorite forms of physical activity—were out of the question. At first, his spirits remained level—mostly because the whole experience was a blur. Everything was happening so fast and he didn't realize the severity of his condition. But when his hair first started to fall out in the shower, reality struck. And for the first time, he cried.“Clumps of hair were coming out on my hands,” Nestor says. “And I was kind of like, ‘What the hell is that?’ That image did it for me in that moment. Like, ‘Holy crap this is real. I’m a freaking cancer patient.’” * * *On a recent, sunny Saturday morning in May, Nestor is back on the Al Buehler Trail around the Washington Duke Inn golf course. Since the 100-miler, the Puerto Rico native has mostly run a few miles a week outside of his house. But on this day, he is revisiting the three-mile trail where he used to usually run before he had to start training on longer trails.