"We expect he'll be fine. He's been playing golf, shooting his episodes and doing real well," manager Robert Malcolm told the New York Daily News for Thursday editions.
Orbach, 69, starred for 12 seasons in the original "Law & Order" series, but left to head the spin-off "Law & Order: Trial by Jury," set to debut next year.
So far, Orbach's illness has not disrupted production of the new show in any way, producer Dick Wolf said.
Malcom said Orbach has been receiving treatment since spring, but declined to discuss how advanced the illness is or the nature of the treatment.
"We expect him to make a full and swift recovery, and while he is receiving treatment, we will work around his schedule," Wolf told the News.
Orbach began playing Detective Lennie Briscoe in 1992, the original show's third season.
Born in the Bronx, he was in the original cast of the off-off-Broadway hit "The Fantasticks" and has appeared in such films as "Dirty Dancing," "Prince of the City" and "Crimes and Misdemeanors."