The 29-year-old inside centre, who has 19 test caps, was diagnosed with leukaemia last August, a diagnosis which rocked his team mates and prompted a number of them to shave their heads in a show of support.
Lealiifano underwent two chemotherapy treatments and then a bone marrow transplant late last year after his sister proved to be a match for donation.
"The doctors said the transplant was a success and everything is looking good in there and the cancer isn't showing up so I'm in remission at the moment but there is still a ways to go," Lealiifano told the Canberra Times.
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"It's a massive milestone today (on Saturday) because that's the time frame they sort of give you, 100 days after the transplant gives you a rough idea of where you stand, so to be cancer-free is quite amazing and why I've got a big smile on my face."
Lealiifano was named as co-captain of the ACT Brumbies this season but is unlikely to play at all, with lock Sam Carter leading the side on the field.
The Brumbies open their Super Rugby season against the Canterbury Crusaders in Christchurch next Saturday.
(Reporting by Greg Stutchbury; Editing by Nick Mulvenney)
