Ethan Zohn Ethan Zohn

Ethan Zohn's cancer has returned.

The former Survivor winner was diagnosed with a rare form of Hodgkin's lymphoma in 2009 and had been in remission since April 2010. Doctors told him of the relapse on Sept. 14.

"It's localized in my lung area," Zohn tells People. "But it's good that it's not all over my body."

Check out photos of Ethan Zohn

On Oct. 18, Zohn, 37, began a "smart" form of chemotherapy that only targets cancerous cells, and he will not lose his hair again. After 12 weeks of treatment, he hopes to undergo another stem-cell transplant from one of his brothers — but doctors won't tell him which one. "They didn't want me to start treating one differently than the other," he says. "Of course my whole family is taking bets on who it is."Zohn says his girlfriend and Amazing Race partner, fellow

Survivor champ Jenna Morasca, has been "taking it like the rock star that she is."

Amazing Race's Ethan and Jenna: We prefer Survivor

"We're both filled with fear and anger and anxiety and gratitude and frustration. But there's so much love there," he says. "It's this whole spectrum of emotions."Determined not to let the bad news slow him down, Zohn still plans to run Sunday's New York City Marathon to raise money for Grassroot Soccer, his nonprofit organization that promotes HIV/AIDS education."I want people to know that you can still live a fulfilled life and move forward," he says.