Doctors consider next treatment for McCain's brain tumor

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Senator John McCain (3TV/CBS 5 file photo) Senator John McCain (3TV/CBS 5 file photo)
WASHINGTON (AP) -

Sen. John McCain's tumor is one of the most aggressive forms of brain cancer, and his doctors are determining next treatment options even as the senator, in a tweet, promised his colleagues in Congress he'd "be back soon."

McCain underwent surgery last week to have a blood clot removed from above his left eye, and that clot turned out to be a sign that a tumor called a glioblastoma had begun growing.

[READ MORE: Sen. John McCain diagnosed with brain cancer]

Here are some things to know about glioblastomas.

Aggressive cancer

McCain's doctors at the Mayo Clinic said they managed to remove all of the tumor that was visible on brain scans, and patients tend to fare better when that happens.

But this kind of tumor, formally known as a glioblastoma multiforme, is aggressive and sneaky. It puts out microscopic roots that go deeper into brain tissue, explained Dr. Joshua Bederson, chairman of neurosurgery at Mount Sinai Health System in New York, who has no direct knowledge of McCain's care.

[WATCH: Barrow neurosurgeon explains McCain's diagnosis]

Still, a tumor above the eye is in a location, called the frontal lobe, that permits removal with far less risk of damage to language, motor and other brain functions than in many deeper areas, he noted.

Surgery doesn't cure

McCain's Mayo doctors said the senator's next treatment options may include a combination of chemotherapy and radiation.

That's standard, and can take weeks to months. Even among those who respond to initial treatment, the cancer can come back, and often within 12 to 24 months. Th/story/35906168/mccains-surgery-anything-but-minore American Cancer Society puts the five-year survival rate for patients over 55 at about 4 percent.

That said, "patients with certain types of mutations or genetic profiles can live longer," five years or more, cautioned Dr. Michael Lim, a Johns Hopkins University neurosurgeon.

He estimates that subset accounts for about 10 percent of the newly diagnosed, and doctors can tell who they are only if pathologists do special molecular testing of removed tumor cells.

Mount Sinai's Bederson tells his own glioblastoma patients that he knows they'll look up the grim statistics, but he wants them to remember that some people do beat the odds for long periods.

"It's a small number. But that's the hope my patients have when they leave my office," he said.

Symptoms

Brain tumors, including glioblastomas, frequently are diagnosed only after the patient suffers symptoms such as headaches or seizures. Depending on where in the brain the tumor is putting pressure, and how large it is, symptoms also sometimes include one-sided weakness or speech difficulties.

McCain's office hasn't said if he reported any symptoms, instead saying he had the blood clot removed after a routine physical exam.

[RELATED: McCain's surgery anything but 'minor']

[RELATED: The absolutely remarkable life of John McCain]

Tumors in the frontal lobe tend not to cause symptoms until they're fairly large, Lim said.

Blood clots and cancer

Sometimes blood clots, too, are an early sign of a brain tumor. Rapidly dividing tumor cells need a blood supply to support their growth, and tap into blood vessels that become leaky.

Where the leak and subsequent clot occurred in the brain would determine if there were any temporary symptoms from that bleed itself, Lim explained.

How often it strikes

Glioblastomas (GLEE'-oh-blas-TOH'-muhs) are most common in adults. According to the American Brain Tumor Association, an estimated 12,390 cases are expected to be diagnosed this year.

McCain is a long-term survivor of melanoma, a deadly skin cancer. But doctors classified this new cancer as a "primary tumor," meaning it's not related to his former malignancies.

New approaches

Scientists are testing a variety of new approaches to treat glioblastomas, and both newly diagnosed patients and those with recurrent disease often are advised to consider options offered in clinical trials .

Several attempts aim at spurring the patient's immune system to attack the tumor, in varying ways. In a very early study of a potential vaccine approach, six of 16 glioblastoma patients lived longer than eight years, said Dr. John Yu of Cedars-Sinai Medical Center in Los Angeles. He said researchers are hunting funding for a larger study.

Also being attempted is CAR-T cell therapy, where doctors genetically engineer a patient's immune cells to better attack their tumor, and combinations of other immunotherapy drugs known as checkpoint inhibitors that make it harder for tumors to evade an immune attack.

Recently a cap-like device that makes electric fields to fight cancer has been shown to improve survival odds for people with glioblastomas.

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