Ex-President Joe Biden's son Hunter says his father's cancer has spread and is painful. (AP PHOTO)Ex-President Joe Biden's son Hunter says his father's cancer has spread and is painful. (AP PHOTO) Credit: AAPFormer US President Joe Biden’s prostate cancer has spread beyond his bones and is very painful, his son, Hunter Biden, said in an interview with the BBC. “The cancer has spread, metastasised into his bones and further,” Hunter Biden told BBC’s Newsnight, according to video posted online on Friday. A spokesman for the 83-year-old Democrat declined on Saturday to comment on Hunter Biden’s interview.