The senator underwent surgery to remove a blood clot on Friday at Mayo Clinic Hospital in Phoenix. Lab results from that surgery confirmed the presence of brain cancer associated with the blood clot.

Glioblastoma is a particularly aggressive tumor that forms in the tissue of the brain and spinal cord, according to the American Brain Tumor Association.

A pathologist was in the operating room during the procedure, a minimally invasive craniotomy with an eyebrow incision, said his doctor, who added that the surgery lasted about three to four hours. Post-surgical brain scans show the tissue causing concern has been completely removed.

McCain is recovering "amazingly well," according to a statement from his office.