Democratic presidential candidate Barack Obama said his grandmother died Monday.

Madelyn Payne Dunham, 86, helped to raise Obama, and had not been well for a long time. She broke her hip recently. But Obama said Monday she died of cancer.

He announced the news in a joint statement with his sister Maya Soetoro-Ng.

"It is with great sadness that we announce that our grandmother, Madelyn Dunham, has died peacefully after a battle with cancer. She was the cornerstone of our family, and a woman of extraordinary accomplishment, strength and humility. She was the person who encouraged and allowed us to take chances. She was proud of her grandchildren and great-grandchildren and left this world with the knowledge that her impact on all of us was meaningful and enduring. Our debt to her is beyond measure.

"Our family wants to thank all of those who sent flowers, cards, well-wishes and prayers during this difficult time. It brought our grandmother and us great comfort. Our grandmother was a private woman, and we will respect her wish for a small private ceremony to be held at a later date. In lieu of flowers, we ask that you make a donation to any worthy organization in search of a cure for cancer."

Obama said he learned of her death Monday morning while he was campaigning in Jacksonville, Fla. He said he planned to go ahead with campaign appearances before Election Day on Tuesday.

In a campaign ad this year, Obama described Dunham as the daughter of a Midwest oil company clerk who "taught me values straight from the Kansas heartland" -- things like "accountability and self-reliance. Love of country. Working hard without making excuses. Treating your neighbor as you'd like to be treated."

Obama recognized Dunham when he accepted the Democratic presidential nomination at the party's convention in Denver.

"She's the one who taught me about hard work. She's the one who put off buying a new car or a new dress for herself so that I could have a better life. She poured everything she had into me," he said.

Obama broke away from campaigning in October and flew to Hawaii in order to be with Dunham after she fell.

Obama said the decision to go to Hawaii was easy to make, telling CBS that he "got there too late" when his mother died of ovarian cancer in 1995 at 53, and wanted to make sure "that I don't make the same mistake twice."