The star has previously spoken about the shock of the diagnosis, which came on the same weekend that her father died from cancer.
In her new autobiography Don't Stop Believin', she said that she strongly believes this will be her "final round" with cancer, even though she will have to monitor her health for the rest of her life.
The four-time Grammy victor, who will turn 70 on September 26, told Australian news program "Sunday Night" doctors found a tumor in her lower back in 2017.
The courageous star told Sunday Night that she has undergone radiation therapy, and is also using natural remedies to help cure her.
The Grease star was diagnosed with breast cancer in 1992, and in 2013, while being treated following a minor auto accident, was found to have cancer in her shoulder.
In 2013, she was diagnosed with cancer in her shoulder after she was involved in a minor vehicle accident.
That time, the actress chose not to tell the public.
"I believe I will win over it", Newton-John said.
Newton-John has made a decision to treat this cancer with modern medicine and natural remedies. But in recent years, it's her fight against cancer that's been in the headlines.
She bounced back and returned to the stage, but last month, she had to cancel two speaking appearances amid reports suggesting she was sick again. I see as part of my mission.
Newton-John said that her husband John Easterling had been growing the plant, something she said he could do legally in California, where the couple live. "They help with pain, they help with sleep".
Newton-John was one of the most successful vocalists of the 1970s, racking up country-pop and soft rock hits like "I Honestly Love You" and "Let Me Be There".
"There are other people out there doing much, much worse than me", she adds. "The first time I talked about it and the second time I thought it wasn't something I really need to share with people". I have a wonderful husband.