The Grease star, 69, told Australian TV show Sunday Night she was now using medicinal marijuana and other natural remedies.
Newton-John survived her initial breast cancer diagnosis in 1992 but revealed that it had returned in 2013.
A third diagnosis, of a tumour in the lower back, was made last year.
The new diagnosis is stage 4 breast cancer that has metastasized to the spine.
In the emotional interview on Sunday Night, she said: "I'm one of millions in this fight. I shouldn't say fight... in this journey.