BOSTON -- Sen. Edward M. Kennedy is undergoing a six-hour "aggressive surgery" Monday at Duke University Medical Center in North Carolina.

The 76-year-old Democrat was diagnosed with a malignant glioma last month after he suffered a seizure at his Cape Cod home. Dr. Allan Friedman, who is known for his research in the field, started the surgery at about 9 a.m.

Dr. Timothy Johnson Explains Surgery | Well-Wishers React To Surgery | Kennedy Sails Before Surgery

Doctors must balance removing as much of the tumor as possible without harming healthy brain tissue. In many cases, the patient is brought back to consciousness while vital areas, such as those controlling speech, are worked on, according to medical experts.

Kennedy expects to remain at the hospital to recuperate for about one week before he starts radiation and chemotherapy at Massachusetts General Hospital.

"Over the past several days, Vicki and I, along with my outstanding team of doctors at Massachusetts General Hospital, have consulted with experts from around the country and have decided that the best course of action for my brain tumor is targeted surgery followed by chemotherapy and radiation," Kennedy said in a statement.

Kennedy's son, Rep. Patrick Kennedy, flew to North Carolina on Sunday night to be with his father for the surgery, Robin Costello, a spokeswoman for the Rhode Island representative said.

Friedman is responsible for more than 90 percent of all tumor resections and biopsies conducted at Duke, according to Duke's Web site. He is head of the Laboratory of Neurosurgical Oncology and an Associate Chief of the Preuss Laboratory for Brain Tumor Research.

Dr. Timothy Johnson said that the senator could be undergoing so-called awake surgery, which is the kind of surgery often performed on patients with Kennedy's type of brain tumor.

"They keep the patient awake while they try to remove as much of the tumor as they can, safely. They do it while the patient is awake so that the patient can, in a sense, guide them as to where they are and what the impact of their probing or removal is at that point," Johnson said.

Johnson said that Duke University Medical Center is known for being aggressive beyond what many other centers will do when it comes to brain cancer.

"It doesn't surprise me that (Kennedy) is there," Johnson said. "He will come back to the Mass General to have what is the more traditional therapy for this kind of brain cancer, which is a combination of an oral chemotherapy drug and radiation, presumably, over a six-week period."

The senator said that he's been humbled by the outpouring of support and is strengthened by well-wishers' prayers and looks forward to getting back to work.

"I am deeply grateful to the people of Massachusetts and to my friends, colleagues and so many others across the country and around the world who have expressed their support and good wishes as I tackle this new and unexpected health challenge," Kennedy said. "After completing treatment, I look forward to returning to the United States Senate and to doing everything I can to help elect Barack Obama as our next president."

One day before his surgery, Kennedy, his wife and their dogs went sailing off Hyannisport at about 2:30 p.m. Sunday.

News of Kennedy's surgery traveled fast in Massachusetts. Visitors at the John F. Kennedy Presidential Library in Boston offered their well wishes.

"I know he was diagnosed with brain cancer and they were looking at different options, but I didn't realize he was going to be brought down to Duke so fast and have the surgery this quickly," visitor John Hickey said.

"It is a little shocking. We thought he may have a little time before anything had to happen to help him get better," visitor Barbara Ward said.

Ed Ward's friend died of brain cancer one year after surgery.

"Each of these cases, I understand, is different. There certainly can be the impact of prayer. A lot of people are praying for Sen. Kennedy, so we just hope for the best," he said.