Illness forcing Maura Tierney from 'Parenthood' series

NEW YORK -- Maura Tierney says she is dropping out of the new NBC series "Parenthood" to continue her treatment for breast cancer.

In a statement Thursday, she expressed disappointment at not being part of the show, but said she and her doctors remain confident about the outcome of her treatment.

Tierney had filmed the pilot episode for the series, which was scheduled to premiere this month. But she was sidelined in July, after a tumor was found in her breast, requiring surgery. Production never resumed.

Another new series, the medical drama "Mercy," will premiere this fall instead.

"Parenthood," based on the 1989 movie that starred Steve Martin, is now set to debut midseason.

Tierney's role -- that of a financially strapped single mother who returns home to her parents -- is expected to be recast.

NBC expressed sadness at Tierney leaving the series, but added, "our main concern is for her quick and full recovery."

Tierney, 44, was a longrunning cast member of the NBC drama "ER" and recently has been seen on the FX drama "Rescue Me."