Singer Olivia Newton-John has postponed a string of Las Vegas shows to be with her older sister, Rona, who has been diagnosed with brain cancer.

Newton-John, 64, who herself survived breast cancer nearly 20 years ago with chemotherapy and a mastectomy, said in a statement that she "received the very sad news" about her sister and "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."

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Rona Newton-John, 69, a former actress who appeared on "The Benny Hill Show" in the 1970s, was married to her sister's "Grease" co-star, Jeff Conaway, from 1980 to 1985. He was stepfather to her son Emerson, 38, a race-car driver most recently in the Firestone Indy Lights Series.

Olivia Newton-John had been scheduled to perform at the Flamingo Las Vegas hotel and casino, substituting for Donny & Marie Osmond's away dates, reported the Las Vegas Sun.