The actress, best known as the sarcastic Abby Lockhart in the long-running hit medical drama 'ER', confirmed she had discovered a cancerous tumour in her breast and needed surgery in July 2009.

As a result, Tierney had to leave the new American series 'Parenthood' she was set to star in to undergo treatment.

In a statement Tierney's spokesperson said: "Ms. Tierney and her doctors remain confident that the outcome of her treatments will be positive."