Joe Biden is receiving radiation therapy for his prostate cancer, a spokesperson for the former US president said.
He was diagnosed with an "aggressive form" of prostate cancer that had metastasised to his bones in May.
"As part of a treatment plan for prostate cancer, President Biden is currently undergoing radiation therapy and hormone treatment," the spokesperson said.
The spokesperson added the radiation treatment is expected to continue for five weeks and is a new stage in his level of care.
Mr Biden, who turns 83 next month, underwent a procedure known as Mohs surgery to remove cancerous cells from his skin in September.
In May his team said the illness was aggressive but hormone-sensitive, meaning it was likely to respond to treatment.
"Cancer touches us all. Like so many of you, Jill and I have learned that we are strongest in the broken places," Mr Biden, whose son Beau Biden died of cancer in 2015, said at the time in a post on X.
"Thank you for lifting us up with love and support."
Prostate cancers are graded for aggressiveness using what is known as a Gleason score.
The scores range from six to 10 and cancers rated from eight to 10 behave more aggressively.
Mr Biden’s office said his was scored as a nine.
Last month Mr Biden had surgery to remove skin cancer lesions from his forehead.
The 82-year-old Democrat left office in January after dropping his bid for re-election six months earlier.
His exit followed a disastrous debate against Donald Trump and came amid concerns about Mr Biden's age, health and mental fitness.
Mr Trump defeated Democrat Kamala Harris, who was Mr Biden's vice-president.
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