"They're happy with the progress of the entry process, and now [doctors] can begin to get rid of the tumor," the figure skater's rep, Michelle Thornbury, told People.com of the surgery.
Hamilton, now 51, has battled cancer for more than a decade. In 1997, he was diagnosed with testicular cancer and beat it before returning to the rink. And in 2004, he learned that he had a brain tumor, called craniopharyngioma, which if left untreated could have resulted in permanent blindness. Gamma radiation was thought to have removed all of the tumor, but it eventually reappeared.
Hamilton is expected to remain in intensive care for several days before returning home next week.