Olivia Newton-John says she has breast cancer and is canceling her June tour.

Olivia Newton-John, who was first diagnosed with breast cancer in 1992, announced Monday she is “reluctantly” postponing some tour dates because her cancer has metastasized to her lower back.

Newton-John said on her Facebook page and her website that the recent back pain she has experienced, and which caused her to postpone the first half of her concert tour, has spread to her sacrum, the triangular bone in the lower back between the two hip bones.

Her publicist, Michael Caprio, confirmed the announcement.

Newton-John, 68, said she is postponing June dates in the U.S. and in Canada to undergo treatment, including a short course of photon radiation in addition to “natural wellness therapies.” She said she is “confident she will be back later in the year, better than ever, to celebrate her shows.”

“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,” said the Aussie singer, who first catapulted to pop-icon status in 1978 when she danced and sang beside John Travolta in Grease.

Caprio said ticket buyers for the upcoming concerts should contact venues directly about refunds, and that rescheduled dates will be posted at in the coming weeks.

Newton-John, who had her first chart success in 1971 with a cover of Bob Dylan’s If Not For You, has been a pop star ever since, surviving personal losses and health threats. Her sister Rona died of brain cancer in 2013, and she herself battled back from a breast cancer diagnosis through most of the 1990s.

That experience helped make her almost as famous for her cancer advocacy as her best-selling songs.

In December the four-time Grammy winner…