Irish American actress Maura Tierney will undergo surgery for breast cancer.

Tierney, who played nurse-turned-doctor Abigail Lockhart on ER for 10 years, said she is optimistic about the outcome.

"I have discovered a tumor in my breast which requires surgery," she said. "I will not know either my exact diagnosis or course of treatment until that surgery is performed.

"My doctors have all assured me this is a very treatable condition. I'm very optimistic as to the outcome and want to thank everyone who has sent positive thoughts and support. I look forward to going back to work soon."

Tierney, whose grandparents are from County Leitrim, grew up in South Boston, home to a large Irish Catholic population.

Tierney's cancer operation has forced NBC to delay production of its new family drama "Parenthood," which stars Tierney and was scheduled to premiere this autumn.

Tierney was a big hit in last year's Tina Fey hit "Baby Mama," and she played Jim Carrey's wife in "Liar Liar."