"[Biden] did not develop it in the last 100, 200 days. He had it while he was president," oncologist Ezekiel Emanuel said Monday on "Morning Joe."

Prostate cancer is the leading cause of cancer diagnosis in men in the U.S. and the second leading cause of cancer death, according to the American Cancer Society. About one in eight men will be diagnosed with prostate cancer, and about one in 41 will die of prostate cancer.

The former president has stage 4 prostate cancer that has spread to his bones. This type of prostate cancer is treatable, but not curable, experts say.