Lt. Gov. Catherine Baker Knoll suffers from a rare cancer that usually is slow-growing, according to medical experts.

Mrs. Knoll, 77, disclosed Wednesday that she is being treated for a form of cancer she termed neuroendocrine illness.

In statements posted on her Web site and released by her office, she said she was diagnosed earlier this summer during a routine medical examination.

"I was surprised by the diagnosis because I feel so good," she said, noting she had no symptoms.

She said her treatments would continue and "the outlook is good." She expects to work a full schedule.

Since the cancer was discovered in July, Mrs. Knoll has had chemotherapy and radiation treatments, said Salvatore Sirabella, her chief of staff. He said she has been working from home for about a month.

"She has a lot of energy," he said, noting she participated by phone yesterday in a state Board of Pardons meeting.

In a statement issued yesterday, House Speaker Dennis O'Brien applauded her plans to continue presiding over the Senate and fulfilling her other duties.

In a separate statement, Gov. Ed Rendell said that he and his wife, Marjorie, were "not surprised that she is fighting back and continuing to serve the citizens of our commonwealth."

Neuroendocrine cancer includes a group of tumor types that can arise from neuroendocrine cells that exist throughout the body.

Those cells secrete hormones that help in food absorption, blood clotting or other needs, including control of calcium and blood sugar levels. Some neuroendocrine cancers lose the ability to secrete hormones, said Dr. Sally E. Carty, chief of endocrine surgery at the University of Pittsburgh Medical Center.

Only 1,000 to 3,000 new cases of the cancers occur in the United States each year, Dr. Carty said.

About 70 percent of cases begin in the gastrointestinal tract, though the tumors can also be found in the lungs or other areas of the body, said Dr. Dulabh K. Monga, an assistant professor at Allegheny General Hospital's cancer center.

Common sites include the adrenal glands, pancreas, chest and neck, Dr. Carty said. Mrs. Knoll has not indicated where her cancer was found.

Dr. Monga said that patients typically have no symptoms when the cancer is discovered, often through diagnostic scans for other conditions.

Surgery is the preferred treatment. About 30 percent to 40 percent of patients respond to chemotherapy, she said, noting the tumors are often resistant to radiation therapy.

If the cancer spreads to the liver, doctors can use injections to block the blood supply to the tumors, she said.

For patients with an aggressive form of the cancer, life expectancy is about two or three years, she said. But 70 percent to 80 percent of patients have more indolent forms of the disease and can live 10 to 15 years, she said.

The disease tends to progress very slowly, "where the patient feels well much of the time," Dr. Carty said. It "may not always be curable, but patients can live with the tumors over the years."

Dr. Carty noted that secretions from the tumors can cause problems. Gastrin, for example, can cause stomach ulcers, and insulin can cause low blood sugar. But those and other problems often can be treated with medication, she said.

The type of treatment used would depend in part on where the tumor started and the hormones it secreted, she said.