The senator has been recovering at home after being told he had a malignant brain tumor. The patriarch was rushed to the hospital May 17 after he suffered a seizure.
"All we know in our family is when doctors give us terrible news, we don't believe it," Kennedy told news reporters. "We fight it, and we've managed to defy the odds every time."
The Democratic congressman's sister, Kara Kennedy, recovered from inoperable lung cancer, The Boston Globe said Wednesday, while his mother, Joan Kennedy, was treated for breast cancer in 2005. Edward Kennedy Jr., his brother, lost a leg to bone cancer in 1973. Patrick Kennedy had a non-cancerous tumor removed from his spine in 1988.
The congressman said the senator was in good spirits.
"My dad is terrific," he said. "If you've seen him the last couple days, you've seen a very happy sailor."