McMahon was diagnosed in Santa Monica, Calif., with acute lymphatic leukemia in May and underwent the stem-cell transplant in August.

"I have a doctor's appointment every week and they check my blood counts," McMahon told MTV.com. "Everything has been good, and then in another 50 days or so they'll test my bone marrow."

McMahon is rail-thin, hairless and exhausted, MTV said.

"This is definitely a little bit of a slower process than just doing the chemo, because you're essentially adopting a new immune system," he explained.

McMahon returned to the studio last week and cut a holiday single, which will most likely turn up on a compilation.

He said Something Corporate will pick up again next year, but in the meantime he plans to promote his solo album, "Jack's Mannequin: Everything in Transit," which came out Aug. 23, the same day he had his transplant.