In this Nov. 2, 2016, file photo, actress and singer Olivia Newton-John attends the 50th annual CMA Awards in Nashville, Tenn. (Photo by Evan Agostini/Invision/AP, File)
Olivia Newton-John is remaining positive after being diagnosed with breast cancer for a second time, declaring she will be "better than ever".
The Australian singer and actress, who became a crusader against cancer with the world-leading Olivia Newton-John Cancer Wellness and Research Centre in Melbourne following her initial battle 25 years ago, had been battling back pain on her current US and Canadian concert tour.
The 68-year-old announced on her Facebook page on Tuesday that pain turned out to be breast cancer that has metastasised to the sacrum, a bone in her lower back.
Newton-John said she is confident she will "be back later in the year, better than ever, to celebrate" on her tour.
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 wrote on Facebook.
To help raised funds for the centre, Newton-John led a three-week, 228km walk along the Great Wall of China in 2008.
She has also released multiple albums where sales benefited breast cancer research, including 2005's Stronger Before, 2006's Grace and Gratitude and 2012's This Christmas album with John Travolta.
Newton-John has kept up a hectic concert schedule in recent years, including high-paying residencies in Las Vegas.
The four-time Grammy-winning entertainer has sold more than 100 million records and also starred in hit films Grease and Xanadu.
She has also endured plenty of tragedy.
Her first marriage to actor Matt Lattanzi ended after 11 years; her Koala Blue US retail venture ended in bankruptcy in 1991; her daughter Chloe battled anorexia; her former boyfriend Patrick McDermott mysteriously went missing in 2005 on a fishing trip off Los Angeles; her sister Rona died from brain cancer in 2013; and a contractor on her Florida property killed himself in 2013.
Newton-John married John Easterling, the founder of a natural remedy firm, in 2008.
© AAP 2017