Zohn was diagnosed with Hodgkin's lymphoma in 2009, but went into remission after enduring three months of chemotherapy.
The reality star learned on September 14 that the disease had reoccurred in his chest, but has not yet spread to other parts of his body.
Zohn soon began another round of chemotherapy and is hoping to have a stem-cell transplant in the coming months, according to People. One of his brothers will donate the needed stem cells, but the exact identity of the donor will remain anonymous.
"The doctors won't tell me which one. They didn't want me to start treating one differently than the other. Of course my whole family is taking bets on who it is," he joked.
Zohn credited his girlfriend and Amazing Race partner Jenna Morasca with helping him deal with the discouraging diagnosis.
"She's taking it like the rock star that she is. We're both filled with fear and anger and anxiety and gratitude and frustration," he said. "There's so much love there. It's this whole spectrum of emotions."
Zohn also tweeted on Wednesday that he will not let fear of the disease consume him, writing: "I have taken all the fear instilled by this disease & transformed it into something fear itself should be afraid of."
Doctors have given Zohn permission to run in the New York Marathon this weekend to raise money for HIV/AIDS prevention.
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