NEW YORK (AP) -- Actress Maura Tierney says she's having surgery to remove a tumor in her breast.

Tierney, who recently wrapped a long-running stint on the NBC medical drama "ER," issued a statement about the surgery on Monday, giving no details on her condition and when she'd due to have the operation.

Says Tierney: "I will not know either my exact diagnosis or course of treatment until that surgery is performed."

Tierney says her doctors assured her "this is a very treatable condition," and she's "very optimistic as to the outcome."

Tierney's setback has delayed production on her new NBC series, "Parenthood," for eight weeks. The network said the medical drama "Mercy" will instead premiere this fall.

NBC is owned by General Electric Co.

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