"I was off chemo," he says. "I was running up to seven miles" in preparation for November's New York City Marathon. "I was happy, I was going out. I went up to Boston to see the family and was feeling great."
Then, on Aug. 26, his doctor called with post-chemo test results and they were not good. "My cancer is back," Zohn, 35, tells PEOPLE. "I have never been so scared in my life, for my life."