NEW YORK -- NBC Universal is confirming that Lauren Graham has joined the cast of NBC's upcoming series "Parenthood." Graham, best known from the longrunning "Gilmore Girls," steps into the "Parenthood" ensemble as a replacement for Maura Tierney. Tierney was forced to drop out of the series this summer after being diagnosed with breast cancer, for which she continues to get treatment. Originally slotted for a fall premiere, "Parenthood" is now set to debut in early 2010. NBC said Monday that production begins in mid-November. Also starring Craig T. Nelson, Bonnie Bedelia and Mae Whitman, the series is based on the 1989 movie that starred Steve Martin.