Olivia Newton-John's Sister, Rona, Diagnosed With Brain Cancer

Olivia Newton-John has revealed that her sister is battling cancer and the "Grease" star will postpone her planned Las Vegas residency to be with her family.

"Entertainment Tonight" reported Monday that Newton-John's older sister, Rona, has been diagnosed with brain 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," the 64-year-old, who was diagnosed with breast cancer more than 20 years ago, told "ET." "I want to thank everyone in advance for respecting our privacy during this difficult time."

The Australian pop star was set to kick off a mini-residency at the Flamingo in Las Vegas, substituting for Donny & Marie Osmond during the duo's away dates, according to The Las Vegas Sun. With her sister's diagnosis, Newton-John will put off the Vegas stint.

"In light of this news, I have decided to postpone my forthcoming Las Vegas residency to spend time with her and our family," she said in a statement obtained by the Vegas Sun.

Newton-John was diagnosed with breast cancer in 1992 after doctors discovered a tumor, People magazine notes. Since then, she has been a spokesperson for cancer awareness and is the proud founder of the Olivia Newton-John Cancer & Wellness Centre in Australia.

Newton-John revealed she found the strength to battle the illness with the help of her loved ones.

"My family and friends were definitely the key to my recovery," she told Everyday Health in 2008. "One thing that I do suggest is that anyone dealing with a life-threatening illness like cancer choose a point person for people to call to find out how you are doing — a sister, brother, mother, father, daughter, son, or close friend. Picking someone close to you to report the news about your health to everyone else frees up time — time you need to heal and become well."