The Denver Post reported Wednesday a biopsy taken before Tuesday's surgery showed the tumor was malignant and Nene's personal manager, Alex Santos, remained cautiously optimistic.
"Nene is feeling better but there is no timetable yet for a return to the court," Santos said. "We're still awaiting results from other exams. It all depends on the results from other exams."
The 6-foot-11 inch Nene, a native of Brazil, took an indefinite leave of absence from the team Jan. 11.
He will go through cancer screening twice a year for the next 10 years but is expected to make a full recovery.
Nene played in just 12 games before his injury was discovered with per game averages of 6.4 points and 6.4 rebounds.
The six-year veteran also missed action earlier this season because of a wrist injury.