Singer and actress Olivia Newton-John has postponed upcoming tour dates after revealing that she is battling breast cancer for a second time.

The Grease star recovered from breast cancer 25 years ago and has devoted her life to helping others with the disease since then.

The 68-year-old had been scheduled to play dates across the US and Canada in June to promote her 2016 collaborative album, Liv On.

The four-time Grammy Award winner will postpone these dates to have treatment and expects to return to the stage later this year.

Olivia Newton-John plans to return to the stage later in the year

Newton-John cancelled a few events last week after suffering from severe back pain. She later discovered her breast cancer had returned and spread to her spine.

A statement posted on her Facebook read: "The back pain that initially caused her to postpone the first half of her concert tour, has turned out to be breast cancer that has metastasized to the sacrum.

"In addition to natural wellness therapies, Olivia will complete a short course of photon radiation therapy and is confident she will be back later in the year, better than ever, to celebrate her shows."

The English-born, Australian-raised star set up the Olivia Newton-John Cancer and Wellness Research Centre in Melbourne after she survived breast cancer in 1992.

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Newton-John appeared on The Ray D'Arcy Show on RTÉ in January when she was in Dublin to play a gig at the National Concert Hall. She spoke about recovering from breast cancer, describing herself as a "thriver".

"I feel healthy and wonderful and thriving starts like I'm moving forward. In the beginning I called myself a survivor but not I'm a thriver", she said.