Olivia Newton-John is postponing her June U.S. and Canadian concert tour dates due to health issues.

The 68-year-old singer shared on Tuesday that 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, Newton-John will complete a short course of photon radiation therapy.

"I decided on my direction of therapies after consultation with my doctors and natural therapists and the medical team at my Olivia Newton-John Cancer Wellness and Research Centre in Melbourne, Australia," Newton-John said in a statement.

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Newton-John says she is confident she will be back later in the year, better than ever, to celebrate her shows.

The Grease actress was first diagnosed with breast cancer in 1992, which had been in remission until this year. In 2007, she talked about her decision to undergo chemotherapy despite initially considering forgoing it to use alternative treatments such as homeopathy and acupuncture.

"Common sense prevailed," she told CNN. "One of my girlfriends said, 'Why would you want to risk even that one cancer cell? You have a child.'"

Newton-John's older sister, Rona, died in May 2013 after a battle with brain cancer. The singer postponed her Las Vegas residency at the Flamingo hotel to be with her family when Rona was first diagnosed one month earlier, and announced plans to start a brain tumor wellness program to honor her beloved sister.

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ET spoke with Newton-John in October 2015, when she talked about collaborating with her daughter, Chloe Lattanzi, on reworking her 1980 hit, "Magic," from the film Xanadu.

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