has been diagnosed with a cancerous brain tumor called a .
His diagnosis was revealed following a procedure last week in which surgeons. Doctors say his tumor was associated with the blood clot.
CBS News medical contributor Dr. David Agus, who is one of the country's top oncologists and director of the USC Norris Westside Cancer Center, joined "CBS This Morning" from Los Angeles on Thursday to talk about McCain's diagnosis and potential treatment plan.
"Glioblastoma is the most aggressive form of brain cancer," Agus told co-host Charlie Rose. "Most people live about 14 and a half months."
Agus said McCain will most likely receive the standard therapy: a combination of oral chemotherapy and radiation therapy for six weeks, followed by a month off from treatment, and then six more months of oral chemotherapy.
Unfortunately, the 80-year-old's form of cancer is difficult to treat. But Agus says the course of therapy is "tolerable," and if McCain receives treatment in Washington, D.C. he could perhaps continue working in the Senate during that time.
"As everybody alludes to, he's tough as nails," Agus said. "And so cancer has certainly a worthy opponent in this one. He's going to take it on."
Glioblastoma is an especially difficult disease, he explained, because "no matter how good the surgery, there is always cancer left behind, and this cancer returns in almost all patients. Right now, they're sequencing the DNA of his cancer to identify what are the 'off switches.' There are drugs that can turn them off."
Agus says there's recent "optimism" about new treatments including "molecularly-targeted therapy and immunotherapy."
When asked about the possibility of finding a cure for the deadly form of cancer, Agus referred to a recent study from Duke University that used ato prompt the immune system to attack glioblastoma. Some of the patients who were involved in the study "have survived many years with this form of treatment," he said.
Clinical trials, simliar to the one that was carried out at Duke, are now spreading across the country at major cancer centers for patients with glioblastoma.
"It doesn't work all the time," Agus noted. "Unfortunately, in our business, nothing really works all of the time. And we don't have a crystal ball, but as much as possible, we try to put patients on experimental therapy when standard treatments have worked."
"Really, for the first time, there's hope in this disease that we can achieve a long-term benefit to patients with some of these newer treatments," he concluded.