Former US president Joe Biden’s prostate cancer has spread to other parts of his body and is causing him pain, even as he continues to speak out on public issues, his son Hunter said in an interview.In a wide-ranging interview with the BBC broadcast late on Friday, Hunter Biden grew emotional as he discussed his father’s condition, describing it as very sad to watch.“The cancer has spread, metastasised into his bones and further,” he said. “It’s very painful and it’s very debilitating in many respects.”Joe Biden, 83, was the oldest man to serve as US president and his age was...