Olivia Newton-John has postponed her upcoming U.S. and Canadian tour after discovering she has cancer, she announced in a Facebook post on Tuesday.

She initially temporarily suspended the first half of her tour due to lower back pain she thought was caused by sciatica before doctors diagnosed her with breast cancer, which has metastasized to the sacrum.

“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 the post.

The singer will complete a short course of photon radiation therapy and natural wellness therapies before she plans to return to tour.

This is the second time that the 68-year-old has battled breast cancer. She was first diagnosed in 1992 on the same weekend that her father died of cancer.

The “Grease” actress had been touring her “Liv On” album, a collection of personal songs about grief and healing, including the loss of her sister Rona to brain cancer in 2013.

Those who bought tickets for the June concerts are encouraged to contact the venues directly about refunds. Rescheduled concert dates will be posted on OliviaNewton-John.com in the next few weeks.