James Harrington spent five years in a grueling battle with the same condition Pittsburgh's mayor has. Barbara Larson beat it in two months.

Their experiences show why it's so hard to predict how Mayor Bob O'Connor will rebound from primary central nervous system lymphoma and the treatment to kill it.

Yesterday Mr. O'Connor got his second dose of methotrexate. That's the chemotherapy drug most commonly used against his lymphoma, though there's no consensus on the best dose or frequency.

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Monitoring for side effects and beginning physical therapy to improve his strength are expected to keep the mayor in the hospital for the balance of the week, his third at UPMC Shadyside Hospital.

That length of stay isn't necessarily a sign of a dire prognosis, doctors agree. Mouth sores and blood clots are among the side effects that can keep a patient in the hospital. For Mr. O'Connor, it has been exhaustion and hiccups.

"I've had people who are feeling great and back riding a motorcycle in two weeks' time, and I've had patients who have been in the hospital for four months," said Dr. Paul Zeltzer, professor of neurosurgery at the University of California, Los Angeles and author of the book "Brain Tumors: Leaving the Garden of Eden."

Both the easy rider and the long-termer can get better, he said.

Probably the best-case scenario is Ms. Larson's. A native of Cherry Grove, Warren County, she was diagnosed with the bran cancer three years ago, at age 60.

She underwent an intravenous chemotherapy course much like the mayor's. "It didn't bother me much at all," said the retired phone company clerk and mother of one.

She said she "obviously got very tired" but she never had to spend more than a few days in the hospital.

Two months of chemotherapy "evidently took care of it," she said, noting her only remaining effect is that she sometimes has trouble walking straight when she's tired.

"I hope your mayor does as well as I did," she said. "I would tell him to just hang in there. Everything is not lost."

Her oncologist, Philip McCarthy of the Roswell Park Cancer Institute in Buffalo, said that until recently a patient with central nervous system lymphoma older than 60 had just a 25 percent chance of living five years. Mr. O'Connor is 61.

Advances in chemotherapy have boosted the chance of living five years to around 50 percent, he said. "If anyone has a great response to [the start of] therapy, that usually bodes well," he said.

Mr. O'Connor's doctors have said that some tumor cells at his four cancerous sites died after just one methotrexate treatment -- viewed as a good result.

Perhaps one central nervous system lymphoma case in five sees "great benefit, usually within a month" from methotrexate, said Dr. James Rubenstein, assistant professor of medicine at the University of California, San Francisco. He sees around two dozen patients with the condition each year.

Of those five theoretical patients, another one will face a much harder road, but will recover, he said. A third will get no result from treatment, and die quickly. "The other two in five are going to have partial responses and never gain full neurological capabilities, and ultimately expire," he said.

Mr. Harrington hopes he's one of the hard-road cases, because it sure hasn't been easy.

In 1999, when the New Fairfield, Conn., resident was 39, his arm went numb on a golf course. A few weeks later, he learned that a golf-ball-sized tumor at the base of his brain was central nervous system lymphoma.

He went through 10 weeks of methotrexate treatment at Northern Westchester Hospital near New York City. Methotrexate and, later, whole-brain radiation, beat the tumor back to an apparently dormant, pea-sized mass. In 2003, though, the cancer came back.

He got admitted to Boston's Dana Farber Cancer Institute for a cutting-edge treatment that involved temporarily removing stem cells while he received a 96-hour dose of methotrexate.

"Coming out of the hospital, I kind of looked like Casper the Ghost," he said. He was homebound for six months. Two years later, he's apparently cancer free.

The ability of patients to return to work while fighting a brain tumor varies widely. It's tougher if the job requires a high level of thinking because tumor cells "may effect the clarity of your thinking and logic," said Dr. Zeltzer.

There are exceptions.

"I had a patient who worked as an IRS regional manager and was able to work right through treatment," said Dr. Virginia Stark-Vance, a neuro-oncologist in the Dallas-Fort Worth area who researched central nervous system lymphoma for the National Cancer Institute in 1993.Others never get back to work.

One thing that's not a significant factor is the type of lymphoma, she said. Mr. O'Connor has the rare T-cell type. Ms. Larson and Mr. Harrington had the B-cell version.

T-cell lymphoma "is a pretty aggressive type of tumor," Dr. Stark-Vance said. "But sometimes, the more aggressive the tumor, the easier it is to treat," because of the distinctive behavior of the cancer cells.

Keys to recovery are the patient's overall health, the use of multiple chemotherapy agents, and the experience of the physicians, experts agreed.

Mr. O'Connor is not known to have complicating medical conditions, other than a duodenal ulcer.

His oncologists, Drs. Stanley Marks and Frank Lieberman, are nationally respected. And their plan includes adding the drug Temodar, which is a less-toxic chemotherapy agent that can enter the brain and spine.

There are two other keys to surviving a long bout, said Mr. Harrington. They are love and attitude.

"My wife is a pillar," he said. "You've got to keep your sense of humor. You have to have faith -- faith and a reason to live. Have those, and you have a shot."