U.S. Democratic presidential nominee Senator Barack Obama (D-IL) addresses a campaign rally in Jacksonville, Florida, Nov. 3, 2008.

WASHINGTON, Nov. 3 (Xinhua) -- U.S. Democratic presidential nominee Barack Obama's grandmother, Madelyn Dunham, died of cancer on Sunday, Obama and his sister, Maya Soetoro-Ng, said Monday.

"She was the cornerstone of our family, and a woman of extraordinary accomplishment, strength, and humility," their statement said.

"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," it added.

Obama and Soetoro-Ng asked that donations be made for the search for a cure for cancer in lieu of flowers.

He left the campaign trail for two days in late October to visit Dunham in Hawaii.

Obama spoke about his grandmother often on the stump, describing her as an integral figure in his youth who struggled against the glass ceiling in to make a better life for him.

"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," he said in his acceptance speech at the Democratic National Convention in August.

"She poured everything she had into me. And although she can no longer travel, I know that she's watching tonight, and that tonight is her night as well."

U.S. voters will choose their new president from Obama and Republican presidential nominee John McCain on the Election Day of Nov. 4.