The 'Grease' star has "reluctantly" postponed her planned performances next month in the US and Canada after learning the life-threatening disease has spread to her sacrum.
The 'Hopelessly Devoted to You' singer had already pulled the first half of her 'Liv On' tour after suffering from back pain, but has now learnt that it was the cancer.
She has vowed to fight the disease with the help of her own Olivia Newton-John Cancer Wellness and Research Centre based in Melbourne, Australia.
The actress will be helped by natural therapists, though she will have to undergo a "short" course of radiation therapy.
On her treatment plan, she said: "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."
Olivia has promised she will be back fighting fit and will reschedule her shows soon.
A statement posted on the star's Facebook page on Tuesday night (30.05.17), read: "Olivia Newton-John is reluctantly postponing her June U.S. and Canadian concert tour dates. 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.
There will be no interview requests accepted at this time as Olivia’s focus is on her treatment and healing. Ticket buyers for the upcoming concerts should contact venues directly about refunds. Rescheduled concert dates will be posted at OliviaNewton-John.com in the coming weeks. (sic)"
Olivia was previously diagnosed with breast cancer 25 years ago in 1992 and underwent a mastectomy.
The 'Psychical' hitmaker – who has 31-year-old daughter Chloe with her ex-husband Matt Lattanzi – previously said fighting cancer "taught her compassion".
She said: "I am grateful for the experience because without it I would not have done many of the things I have done in my life. It's taught me compassion for those going through difficult times."