By Joseph Ax and Nandita Bose

(Reuters) -Former U.S. President Joe Biden has been diagnosed with an "aggressive form" of prostate cancer that has spread to his bones, his office said in a statement on Sunday.

Biden, 82, was diagnosed on Friday after experiencing urinary symptoms, and he and his family are reviewing treatment options with doctors, according to the statement.

"While this represents a more aggressive form of the disease, the cancer appears to be hormone-sensitive which allows for effective management," his office said.

Cancers that have spread, or metastasized, are considered Stage 4, the most advanced. Most prostate cancers are detected at an earlier stage.

According to the Centers for Disease Control and Prevention, of the 236,659 cases of prostate cancer diagnosed in 2021, 70% were diagnosed before the cancer had spread beyond the prostate. About 8% of new prostate cancer diagnoses that year involved advanced-stage disease.

Biden's physical health and mental acuity drew scrutiny during his 2021-2025 presidency. He abruptly ended his bid for reelection last July, weeks after a halting performance during a debate against Republican Donald Trump prompted panic among his fellow Democrats.

President Trump, who has repeatedly berated Biden since taking office in January, expressed sympathy on Sunday for Biden and his wife, Jill, in a post on his social media platform Truth Social.

"Melania and I are saddened to hear about Joe Biden's recent medical diagnosis," he wrote, referring to first lady Melania Trump. "We extend our warmest and best wishes to Jill and the family, and we wish Joe a fast and successful recovery."

Biden's office said the cancer scored a nine out of 10 on the Gleason score grading system, which is used to help determine the aggressiveness of prostate cancer.

Dr. Herbert Lepor, an urologist at NYU Langone, said a score of nine is "very high risk," but added that many men can live "five to 10 years and beyond" even with metastatic prostate cancer.

"Over the last decade, there have been many advances in the treatment of advanced prostate cancer," he said.

Dr. Chris George, the medical director of the cancer program for the Northwestern Health Network, said prostate cancer is no longer curable once it spreads to the bones but that there are treatments that can control it.

BIDEN, TRUMP OLDEST TO WIN PRESIDENCY

Biden was the oldest person to win the U.S. presidency at the time of his election in 2020. Trump, 78, broke that record when he defeated Vice President Kamala Harris last year.

Some prominent Democrats have recently acknowledged that it was an error to advance Biden as the 2024 nominee, given widespread concerns among voters about his age. Long before the debate last summer, Reuters/Ipsos polls showed a majority of Americans, including most Democrats, believed Biden was too old to serve a second term.

"It was a mistake for Democrats to not listen to the voters earlier," Democratic U.S. Senator Chris Murphy told NBC News' "Meet the Press" on Sunday morning, before Biden's diagnosis was announced.

Biden has kept a low profile since leaving office, making only a handful of public appearances, including an April speech in which he defended the Social Security Administration against Trump's planned cuts.

He has also defended his legacy in interviews and rejected reporting in two new books that he suffered from cognitive decline during his last year in office.

"They are wrong," he said earlier this month on ABC's "The View," referring to the books' authors.

Biden's diagnosis triggered an outpouring of supportive statements on Sunday from Democrats and Republicans alike.

"Joe is a fighter — and I know he will face this challenge with the same strength, resilience and optimism that have always defined his life and leadership," Harris said in a statement.

Biden lost a son, Beau Biden, in 2015 due to brain cancer.

In 2022, Biden revived an Obama-era program known as Cancer Moonshot, seeking to reduce the death rate from cancer by at least 50% over the next 25 years.

(Reporting by Nandita Bose, Joseph Ax, Steve Holland, Kristina Cooke, Costas Pitas and Nancy Lapid; Editing by Paul Simao, Colleen Jenkins, Rod Nickel, Diane Craft and Lincoln Feast.)