Olivia Newton-John's Sister Battling Brain Cancer

Olivia Newton-John has revealed that older sister Rona has been diagnosed with brain cancer. The former "Grease" star spoke about her sister's strength as well as her own battle with cancer.

"As a cancer 'thriver' myself, as many people are, I am very aware of the importance of love, support and family during this journey she is about to begin," Newton-John told ET. "I want to thank everyone in advance for respecting our privacy during this difficult time."

Newton-John was diagnosed with breast cancer nearly 20 years ago and underwent a partial mastectomy and chemotherapy. She has been incredibly open and honest about her treatment and struggle with cancer, and has been cancer free for several years.

"I learned very quickly how important it was to think positively," she posted on the Olivia Newton-John Cancer & Wellness Center website. "When the second friend I called with the news burst into tears, I thought, 'I don't need this.' I had a sister and friends make the calls, that way I could focus on positive thoughts."

She founded the Olivia Newton-John Cancer & Wellness Center in Melbourne, Australia to help others and offer an alternative to the standardized treatment offered by hospitals.

"More than just treating cancer, it's about providing care and treatment for the whole person, body, mind, and spirit," Newton-John says on the website. The final portion of the center is due to open this July.

"More and more people are affected by cancer. I believe we are a world in desperate need of healing. I'm committed to doing whatever I can. I've always believed that if you go through anything, even something as difficult as cancer, then something good can come out of it," Newton-John added.

Newton-John was scheduled to begin performing at the Flamingo hotel in Las Vegas, but she has postponed the show in order to be with her family during this time.