(CNN) Sen. John McCain , 80, has been diagnosed with a primary glioblastoma, a type of brain tumor, Mayo Clinic doctors directly involved in the senator's care told CNN exclusively. The doctors spoke directly to CNN Chief Medical Correspondent, Dr. Sanjay Gupta.

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.

The senator showed no neurological problems before or after the operation, said his doctors. Though not identified by name, at McCain's request, his doctors were given permission to speak with Gupta, who is also a practicing neurosurgeon.

McCain is now recovering at his Arizona home. He and his family are considering treatment options, which will likely include radiation and chemotherapy, his doctors said.

"The news of my father's illness has affected every one of us in the McCain Family," tweeted Meghan McCain on Wednesday. "It won't surprise you to learn that in all this, the one of us who is most confident and calm is my father."

Routine exam

Doctors discovered the clot during a routine physical exam last week. They said he is very diligent about coming in for scheduled exams and is seen every four months for skin checks due to his history of skin cancer.

He arrived at his early morning appointment, Friday before 8 a.m. and as per usual, looked good, according to a doctor who has been involved in his care for nearly a decade. McCain, described as not being a complainer, did report feeling fatigued, which he attributed to a rigorous travel schedule.

He also told his doctor he had, at times, felt foggy and not as sharp as he typically is. In addition, he reported having intermittent double vision. These symptoms and doctor intuition prompted a CT scan.

When the results came back, McCain, who had already left the clinic, was asked to return for an MRI. Before the operation, his neurological exam was normal, according to his doctor.

The operation began in the late afternoon and the senator was recovering in the ICU by evening. His doctors told Gupta they were amazed at how sharp McCain was when he awoke. He knew what year it was and started cracking jokes. He also made it clear that he wanted to leave the hospital and get back to work, his doctors said.

Showing no signs of cognitive delays, McCain was discharged Saturday and has been recovering at his home since then.

His doctors would not reveal details but said his post operative care is standard.

'Aggressive tumor'

His doctor said McCain was oriented, with good balance and no headaches or seizures.

The clot was over the senator's left eye, not far from the left temple where he was diagnosed with invasive melanoma in 2000. Previously, McCain had three other malignant melanomas removed in 1993, 2000 and 2002. None of these melanomas were invasive. All were declared Stage 0.

However, McCain has been regularly screened by his doctors since 2000.

Gupta was one of a select group of reporters who reviewed McCain's medical records in 2008 when he was campaigning for president.

The surgical procedure McCain underwent is "a significant operation," said Gupta, explaining that a bone underneath the eyebrow had to be removed to do the procedure and then later put back.

"It's a very aggressive tumor," said Gupta. He explained that average survival for malignant glioblastoma tends to be around 14 months with treatment. In McCain's case, additional therapy, including radiation, could not begin until the incision heals, which would be in the next three or four weeks.

Still, one 2009 study reported that almost 10% of patients with glioblastoma may live five years or longer, according to the American Brain Tumor Association.

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"This is the same tumor that Ted Kennedy had," said Gupta.

McCain's diagnosis is the latest chapter in a storied life. Tortured as a Vietnam prisoner-of-war, the maverick politician fell short of the pinnacle of politics with two failed presidential runs. His absence from Washington in recent days has come at a politically inopportune time for a bill repealing and replacing Obamacare. This week, McCain broke ranks and called for discussions with Democrats and a full committee process to finally provide "Americans with access to quality and affordable health care."