President Biden has started a new phase of treatment for an aggressive form of prostate cancer, which includes radiation and hormone therapy, according to new reports on Saturday.

“As part of a treatment plan for prostate cancer, President Biden is currently undergoing radiation therapy and hormone treatment,” the former president’s spokesman said in a statement to multiple news outlets.

The radiation treatment is expected to last five weeks and marks a new stage in his care, a source familiar with the situation told NBC News, which first reported the story. Mr. Biden, who turns 83 next month, has already been on a hormone medication in pill form.

Mr. Biden first announced his diagnosis in May, revealing he had an aggressive form of prostate cancer that had metastasized to his bones. At the time, his office noted that the cancer appeared to be “hormone-sensitive which allows for effective management.”

In his first public comments after the diagnosis, Mr. Biden expressed optimism about his prognosis. “It’s all a matter of taking a pill, one particular pill, for the next six weeks and then another one,” the 82-year-old said in May. “Well, the prognosis is good. You know, we’re working on everything. It’s moving along. So I feel good.”

In a separate interview, he told CNN, “The expectation is we’re going to be able to beat this. It’s not in any organ, it’s in – my bones are strong, it hadn’t penetrated. So, I’m feeling good.”

Mr. Biden’s diagnosis was characterized by a Gleason score of 9 (Grade Group 5), which indicates a high-grade, aggressive cancer likely to grow and spread rapidly. This is the highest-risk category for prostate cancer.

While medical experts not involved in Mr. Biden’s care noted the seriousness of the diagnosis, particularly with metastasis to the bone, they also pointed to significant advances in treatment.

“The fact that Biden’s cancer had spread to the bone is very serious and not curable,” Dr. Benjamin Davies, a professor of urologic oncology at the University of Pittsburgh Medical Center, told CNN in May. However, he added, “There is some good news here in the newer hormonal and chemotherapy therapies … which have shown impressive results and extended the longevity of patients significantly.”

Prostate cancer is the most common cancer among men in the U.S., but it often grows slowly and has a high five-year survival rate of roughly 98 percent, according to the National Institutes of Health.

This is not Mr. Biden’s first recent encounter with cancer. Last month, he underwent Mohs surgery to remove a skin cancer lesion. Following the procedure, his physician stated that “all cancerous tissue was successfully removed” and “no further treatment is required.” In 2023, while still in office, he also had a cancerous skin lesion removed from his chest.