Ethan Zohn: I'm getting better

"Running, cycling, whatever you want me to do. It's easy and helps builds confidence," Ethan Zohn said.

STORY HIGHLIGHTS

• Ethan Zohn had just finished round three of the new chemo drug SGN-35


• "I'm responding very well to the drug," Zohn tells PEOPLE


• He will be rescanned in hopes of undergoing a stem-cell transplant

() -- Battling a , former "" winner Ethan Zohn had just finished round three of the new chemo drug SGN-35 when he got some welcome news from his doctor.

"I'm responding very well to the drug," he tells PEOPLE. "My tumors are reducing. It's not a 100-percent reduction, but my doctor gave me an A-minus so I'll take it."

Zohn, who learned in September that the , hasn't let his treatment slow him down.

In November, he in 4:20 and just completed the Walt Disney World Half Marathon earlier this month alongside longtime girlfriend Jenna Morasca. "I'm not going to stop!" he says, laughing. "Running, cycling, whatever you want me to do. It's easy and helps builds confidence."

Next up for Zohn is Cycle for Survival, an indoor team cycling event to fund rare cancer research at Memorial Sloan-Kettering Cancer Center in New York, where he is being treated. With plans to cycle at the events on February 4 in San Francisco and on February 12 in New York, Zohn says he is participating in honor of CFS's founder and close friend, Jennifer Goodman Linn, who lost her battle with sarcoma last July.

"This year I really wanted to get involved in honor of Jen and to prove to people that the money raised really does help. The drug I'm on, SGN-35, wasn't available before so I'm living proof," he says. "They've raised $ 12 million since 2007, which is unheard of. I want to do everything I can to help extend Jen's legacy and her vision."

Once he completes a total of six chemo treatments, Zohn will be rescanned in hopes of undergoing a stem-cell transplant from one of his brothers, who is a match. Though he knows the identity of the "winner," he has yet to break the good news to his family and friends.

"The holiday season was fun because I was basically taking bets," he says. "All my friends and family were placing bets so I was living a double life as a bookie."

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