The spokesperson also said that Biden, 82 years old, is receiving hormone therapy to help manage the disease, though no further details were provided.

According to NBC News, which first reported the story, the radiation treatment is expected to last five weeks and represents a new phase in Biden’s medical care.

In May, Biden’s office revealed that he had been diagnosed with an aggressive form of cancer that had spread to his bones. This came after the Democratic politician experienced urinary difficulties, prompting medical tests that discovered small tumors in his prostate.

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At the time, his office said he was suffering from “prostate cancer with a Gleason score of 9 (Grade Group 5),”  one of the highest levels on the scale used to measure cancer severity.

A Gleason score of 9 indicates a high-grade and aggressive cancer, meaning the cancer cells are likely to spread quickly to other parts of the body, according to Cancer Research UK.

A source close to Biden told CBS News (a BBC partner in the U.S.) that the former president is doing well and that the treatment is proving effective. Another source said Biden began receiving radiation therapy several weeks ago in Philadelphia.

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Biden left office in January as the oldest president in U.S. history, after health concerns during his four-year term led him to abandon plans to seek re-election midway through the campaign season.

Kamala Harris, his former vice president, ran as the Democratic Party’s candidate, but lost to current President Donald Trump.

Biden has long been a strong advocate for cancer research. In 2022, he and his wife Jill Biden relaunched the “Cancer Moonshot” initiative, aimed at advancing research and preventing four million cancer deaths by 2047.

According to the U.S. Centers for Disease Control and Prevention (CDC), about 13 out of every 100 men will be diagnosed with prostate cancer at least once in their lifetime.