Former US President Joe Biden started radiation treatments for an aggressive form of prostate cancer diagnosed in May.

“As part of a treatment plan for prostate cancer, President Biden is currently undergoing radiation therapy and hormone treatment,” a spokesperson for Biden said. NBC News reported earlier that the radiation treatment is expected to span five weeks.

Biden also underwent a Mohs surgery to remove cancerous cells from his skin in early September, a spokesperson told NBC News.

When Biden’s prostate cancer was first announced in May, his spokesperson, Kelly Scully, said it had metastasised to the bone and was hormone sensitive.

Because his cancer was hormone sensitive, it could have responded to hormone therapy, which involves stopping testosterone from being made or reaching cancer cells.

Radiation therapy in advanced prostate cancer that has metastasized to the bones can help keep it under control for as long as possible and prevent or relieve symptoms, according to the American Cancer Society.

Prostate issues, including cancer, are common in older men. Biden was the oldest serving president in US history and turns 83 next month.