What is Glioblastoma? Senator John McCain is in for the Fight of His Life

Glioblastoma is an aggressive type of brain cancer, so what’s Senator John McCain’s prognosis? Brian Snyder/REUTERS

News of Senator John McCain's brain cancer diagnosis has brought to public light a difficult disease with an uncertain prognosis. On Wednesday, his office posted a press statement updating the public on his treatment. McCain underwent a procedure at the Mayo Clinic in Phoenix to remove a blood clot above his left eye. The pathology report indicated that the blood clot is linked to a type of brain tumor known as a glioblastoma.

According to the statement, McCain and his family are considering treatment options. "The senator's doctors say he is recovering from his surgery 'amazingly well,' and his underlying health is excellent."

The American Brain Tumor Association says that glioblastoma accounts for approximately 15 percent of all brain tumors. Symptoms include headache, nausea, vomiting and drowsiness, as well as some neurological problems and memory impairment.

Newsweek spoke with Dr. Mark Gilbert, a senior investigator and chief of the Neuro-Oncology Branch, which is a collaboration between the National Cancer Institute and the National Institute of Neurological Disorders and Stroke, about what the former GOP candidate can expect in the coming months and the future of glioblastoma research and treatment.

What is glioblastoma and how is it different from other types of brain cancer?
Glioblastoma is a type of brain cancer which we call primary brain cancer or a primary brain tumor, which designates that it started in the brain. That distinguishes it from what we would call secondary brain cancer or metastatic brain cancer, which is a spread of cancer from another organ. So a lung cancer can spread to the brain as a brain metastasis; that's a secondary brain cancer.

It very rarely spreads outside the nervous system. In my 31 years of doing this, I've had five patients who had their glioblastoma spread outside their brain. That's less than one in a thousand.

That's a really important distinction when you talk to people, because when people hear of family members or friends who have cancer and they get bone scans or CT scans of their chest and abdomen. You don't do that with glioblastoma because it's not going to any of those places.

So if it's not metastasizing, does that mean it's less fatal?
No. Its damage is because it's so infiltrative that you cannot cure it with just surgery.

How is it usually treated?
It's usually treated first with surgery to remove as much tumor as possible that is safe. Because it's the brain, you obviously have to be very careful about what's being removed. There's an area that's tumor, but surrounding that is an area that is infiltrated by tumor. You don't want to be taking out functioning brain that will compromise the neurological functioning. So what you have to do is maximal safe tumor removal. That's the start.

Then the standard treatment is a combination of chemotherapy and a drug called temozolomide, which is an oral drug that is taken every day with radiation. Radiation to the tumor, plus an area of an inch surrounding the tumor because there are microscopic cells that can't be seen in an MRI in the area. After that, patients receive the temozolomide, the chemotherapy alone.

What did McCain's blood clot have to do with the cancer?
These tumors, in order to grow, have to develop their own blood vessels. These blood vessels form so quickly, so they're very fragile, and occasionally one of them will break or hemorrhage into the tumor.

The tumor expands very quickly, and the patient experiences very sudden symptoms. It's not uncommon for a hemorrhage to be the reason a patient comes to the hospital. The brain is an amazing organ, and it can accommodate a lot of change if it's done slowly and gives it time to adjust. When a hemorrhage happens, it usually precipitates something, so either severe headache or change in consciousness or seizure.

What's the prognosis? Does it depend on what stage the cancer is?
They define [McCain's cancer] as a grade four, the highest grade, an aggressive form that unfortunately is incurable. But in some people it can be controlled for years. There are lots of new treatments being tested in clinical trials. When those treatments are proven to be beneficial, they become part of the standard of care.

The senator is 80 years old. Is age a possible factor in survival?
Age is a factor, and older folks don't do as well.

What are the risk factors for developing glioblastoma?
In almost every patient we see, we cannot determine a risk. There are a few genetic syndromes that are associated with an increased risk of brain tumor, but they're really rare. I would say that out of every 100 patients that we see in my practice, one of them may have an underlying genetic syndrome.

What can you tell me about these potential treatments?
There's a whole variety of ongoing studies. People have asked me which treatment is best. If I knew what was best, it wouldn't be experimental or we would use it.

There are different types of clinical trials, but the ones that are most prominent target specific pathways in the cancer cell that are thought to be essential to the cancer's growth and survival. The other big area is immunotherapy.

In the brain tumor field, the immunology is a little more complicated because of the brain itself. The blood-brain barrier and the immunobiology of the brain is different than the rest of the body. It's going to take us extra effort to really understand how to do that and do it the best we can.

Is it possible that the senator could enroll in a clinical trial?
Yes, we always encourage patients to enroll in a trial. There are different types of clinical trials ongoing, but the most promising are the ones that target different pathways in the cancer cell that are thought to be essential to the cancer cell's growth and survival.

McCain has late-stage cancer. In general, what's his prognosis? How long can patients in this stage expect to live?
That's a really difficult question. We can give you averages, but I would argue that no one is average. The median survival is between 15 to 18 months. There are people who don't do that well, and there are those who do.

The big unknown factor is how sensitive cancer is to treatment. But you don't know until you treat them. You can look under the microscope, and we can see two cancers that almost look identical. In one, the prognosis is great, and the other, it's poor.