NEW YORK (AP) – S. Epatha Merkerson, the senior member of the 'Law & Order' cast, is leaving after the show's current 20th season.

Merkerson, who joined the NBC drama in 1993 as New York police Lt. Anita Van Buren, has decided to exit after 16 years, according to a person close to the show who spoke on the condition of anonymity because that person wasn't authorised to speak about cast changes.

Merkerson, who held firm on a series that has seen literally dozens of cast members come and go, has played a strong, no-nonsense supervisor in a Manhattan police precinct, primarily overseeing two detective characters (currently played by her co-stars Jeremy Sisto and Anthony Anderson). But this season, Van Buren's story line has taken a personal turn as she battles cancer, an illness that may figure into her departure from the show. Will Van Buren die?

"Not necessarily," Merkerson told Entertainment Weekly, which first reported her planned exit. "How ever they decide to take her out, it'll be worthy of the character. Either way, it'll be great for me because I get to act it." Early in the 57-year-old Merkerson's career, she played Reba the Mail Lady on 'Pee-wee's Playhouse'. She won Emmy, Golden Globe and Screen Actors Guild awards for her performance in HBO's 2005 film 'Lackawanna Blues'. In February, she won an NAACP Image Award for her role on 'Law & Order'. As Merkerson prepares to take her leave, 'Law & Order' awaits news of whether it will be back next season. In recent years, the series has suffered a ratings slump. A renewal would make it TV's longest-running drama. It currently ties 'Gunsmoke'.