The news comes nearly a year after the former president was forced to drop out of the 2024 US presidential election over concerns about his health and age. He is the oldest person to have held the office in US history.

Biden, then the Democratic nominee vying for re-election, faced mounting criticism of his poor performance in a June televised debate against Republican nominee and current president Donald Trump. He was replaced as the Democratic candidate by his vice-president, Kamala Harris.

Prostate cancer is the second most common cancer affecting men, behind skin cancer, according to the Cleveland Clinic. The US Centres for Disease Control and Prevention (CDC) says that 13 out of every 100 men will develop prostate cancer at some point in their lives.

Age is the most common risk factor, the CDC says.

Dr William Dahut, the Chief Scientific Officer at the American Cancer Society and a trained prostate cancer physician, told the BBC that the cancer is more aggressive in nature, based on the publicly-available information on Biden’s diagnosis.

“In general, if cancer has spread to the bones, we don’t think it is considered a curable cancer,” Dr Dahut said.

He noted, however, that most patients tend to respond well to initial treatment, “and people can live many years with the diagnosis”.

Dr Dahut said that someone with the former president’s diagnosis will likely be offered hormonal therapies to mitigate symptoms and to slow the growth of cancerous cells.

Biden had largely retreated from the public eye since leaving the White House and he has made few public appearances.

The former president delivered a keynote speech in April at a Chicago conference held by the Advocates, Counselors, and Representatives for the Disabled, a US-based advocacy group for people with disabilities.

In May, he sat down for an interview with the BBC – his first since leaving the White House – where he admitted that the decision to step down from the 2024 race was “difficult”.

Biden has faced questions about the status of his health in recent months.

In an appearance on The View programme that also took place in May, Biden denied claims that he had been experiencing cognitive decline in his final year at the White House. “There is nothing to sustain that,” he said.

For many years, the president had advocated for cancer research.

In 2022, he and Mrs Biden relaunched the Cancer Moonshot initiative with the goal of mobilising research efforts to prevent more than four million cancer deaths by the year 2047.

Biden himself lost his eldest son, Beau, to brain cancer in 2015.