Lauren Graham Joins "Parenthood" Cast

Maura Tierney has been forced to drop the "Parenthood" series to undergo breast cancer treatment. The network has confirmed that "Gilmore Girls" star Lauren Graham will be her replacement.

Helen Hunt was approached originally to fill in for Tierney but a deal could not be made.

Tierney, 44, revealed in July that she found a tumor in her breast that required surgery.

The NBC series was due for release during the fall season but is now set to premiere in early 2010. Production will begin in mid-November.

Graham made a Broadway debut in Feb. in the revival of "Guys and Dolls" in NYC as Miss Adelaide.

"Parenthood" will be Graham's first role as a series regular since "Gilmore Girls" in 2007. Also starring alongside Graham will be Craig T. Nelson, Bonnie Bedelia, and Mae Whitman.

The basis of the series derives from the 1989 comedy directed by Ron Howard and starring Steve Martin.

The executive producers of "Parenthood" are Howard, Jason Katims, Brian Grazer and David Nevins.