PHOENIX - Radiation or chemotherapy will most likely be the next step for Arizona Sen. John McCain as he battles a glioblastoma, an aggressive form of brain cancer.

"Sen. McCain is a fighter," said Dr. Michael Berens, the deputy director of TGen and professor in the cancer and cell biology division.

A statement from McCain's office suggests the 80-year-old is weighing his treatment options including radiation and chemotherapy.

"There are courses of radiation therapy and radiation is a very effective way to control the growth," Berens said. "For this tumor in the brain, there are very few (chemo treatments) that can get access to the brain."

The challenge is what's called the blood-brain barrier comprised of many capillaries that protect the brain from any perceived toxins.

Many chemo treatments cannot penetrate that barrier, but there are a few treatments that can.

"We know from many, many, many clinical studies that this treatment plan adds significant days and months for patients that had very good quality of life," Berens said.

The average prognosis for survival is about 15 months after the diagnosis, but Berens stressed every patient is different.

"Yes, it's a battle and the battle has to be fought, but let's go in a supportive mode and have good expectations," Berens said.