Olivia Newton-John Sister: 'Physical' Singer's Older Sibling Rona Battling Brain Cancer, 'Xanadu' Star Postpones Las Vegas Residency

Actress and singer Olivia Newton-John recently announced that her older sister, Rona, has been diagnosed with brain cancer. The 64-year-old Grease star has therefore postponed her upcoming Las Vegas residency at the Flamingo hotel in order to spend time with her sister and other family members. As a cancer-survivor herself and an advocate for cancer research, her sister's diagnosis is clearly her priority right now.

Newton-John battled breast cancer about 20 years ago. She announced in a statement that she heard about her sister's "very sad news." She continued, "In light of this news, I have decided to postpone my forthcoming Las Vegas residency to spend time with her and our family. 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. I want to thank everyone in advance for respecting our privacy during this difficult time."

Olivia Newton-John was diagnosed with breast cancer in 1992, the same weekend that her father died. She had recently released an album, Back to Basics - The Essential Collection 1971 - 1992, but had to cancel her publicity dates in order to deal with her diagnosis. Olivia was also planning her first tour in about ten years since her "Physical" tour, but had to cancel.

Since her diagnosis, Olivia Newton-John has been an avid advocate for Breast Cancer research, which added to her long list of advocacies. In 2008, she raised funds for and founded the Olivia Newton-John Cancer and Wellness Centre in Melbourne, Australia.

Olivia Newton-John has been free of breast cancer ever since undergoing treatment and a mastectomy.

Though tickets have not even gone on ale yet, Newton-John has postponed her residency at the Flamingo in Las Vegas to spend time with Rona. Olivia was set to appear as a replacement for Donnie and Marie Osmond's away dates.