LOS ANGELES, Sept. 11 (UPI) -- Maura Tierney's publicist says the U.S. actress has had to leave the new TV series "Parenthood" because she is undergoing treatment for breast cancer.

Tierney, 44, is best known for her roles on "NewsRadio," "ER" and "Rescue Me."

NBC moved the premiere of its small-screen version of the movie "Parenthood" back after Tierney discovered a tumor in her breast. However, she must now undergo further treatments which conflict with the show's new schedule.

"Maura Tierney regrets that she will not be able to continue her role on 'Parenthood' due to a conflict with the production schedule of the show and her breast cancer treatments," Usmagazine.com quoted her representative as saying in a statement. "Ms. Tierney and her doctors remain confident that the outcome of her treatments will be positive. She is deeply disappointed that she will not be able to rejoin such a highly respected, talented, fun and funny group of actors and wishes to thank Jason Katims and NBC for their patience and support."

"While we are saddened that Maura Tierney won't be able to continue in her current role in 'Parenthood,' our main concern is for her quick and full recovery," NBC said.