Pittsburgh Mayor Bob O'Connor was "comfortable and stable without any side effects" yesterday following a session of chemotherapy, doctors said, and likely will be released from UPMC Shadyside Hospital this weekend.

John Beale, Post-Gazette Dr. Stanley Marks, left, and Dr. Frank Liebermann, of the UPMC Cancer Center, talk about treatment being given to Pittsburgh Mayor Bob O'Connor during a briefing yesterday. Click photo for larger image. Online audio Dr. Frank Lieberman: The mayor is still a little sleepy Dr. Stanley Marks: The mayor's treatment. Dr. Marks: The mayor's ulcer. Dr. Marks: The mayor's current condition. Dr. Lieberman: The mayor's desire to continue his duties. Dr. Lieberman: The mayor may return to work.

Still, doctors described the 61-year-old mayor as very tired, due to multiple medications and tests.

The mayor's administration, meanwhile, didn't budge from the position that there was no need to appoint an acting mayor. Government veterans said there would be political implications to what could be an extended fight for Mr. O'Connor with a rare form of central nervous system lymphoma.

Dr. Stanley Marks, director of clinical services at UPMC Hillman Cancer Center, said the mayor needs rest as his body contends with high doses of the chemotherapy agent methotrexate, steroids, painkillers and frequent tests.

"Even someone who has enormous stamina is going to be exhausted for a few days after that kind of activity," added Dr. Frank Lieberman, chief of neuro-oncology at the cancer center.

The city's charter gives a mayor the option of appointing a department head when he is "temporarily disabled."

"There's no need to do that. If the need arises, the doctors will tell us," said mayoral spokesman Dick Skrinjar.

Starting last night, the mayor got doses every six hours of leucovorin, a vitamin that will protect his normal cells from the methotrexate. Without it, the chemotherapy would be fatal, Dr. Marks noted. Once the methotrexate has sufficiently cleared his system, the mayor will be discharged from the hospital until his next round of that drug, which could occur July 25 or 28.

His neck pain and headaches have improved, and should continue to get better, so his need for painkillers is declining.

According to Hildy Dillon, vice president of patient services disease programs for the Leukemia & Lymphoma Society, most chemotherapy side effects are cumulative.

"Usually people come out of their first cycles of treatment and they feel OK, but later on they might not feel so well," she said. "But some people slide through these things and don't have very many side effects."

On Tuesday, and after each subsequent dose of methotrexate, the mayor will take an oral chemotherapy drug called Temodar daily for seven days. Trials are under way to assess the effectiveness of the drug combination.

"Those studies are still ongoing," Dr. Lieberman said. "But I think there is good reason to believe adding Temodar to the regimen will increase the activity" against the cancer.

Mr. O'Connor will return to the hospital for methotrexate treatments about every two weeks for 10 to 12 weeks.

Psychologically, the mayor has handled the news well, the doctors said.

Dr. Marks said the mayor's medical team started suspecting cancer over the weekend, and told him and his family then.

"Actually, he took it quite well," he said. "He's a hard-nosed, tough guy, and said, 'What are we going to do next?'"

They considered holding off on treatment until after Tuesday's Major League Baseball All-Star Game, but in view of his symptoms, opted to start promptly.

Now talk is turning to how much work Mr. O'Connor should do, and how quickly.

Yesterday, he was "able to read documents, but he's taken a lot of medication that makes him tired," Dr. Marks said.

He slept better Tuesday night than he had in days, Dr. Lieberman said. "We'd like to take credit for that, but really I think it's because his wife got him a better pillow."

The mayor's thinking isn't impaired, he added.

"I don't really see any evidence currently that the tumors that he has are compromising neurologic function," he said. "We're being very careful in designing the therapy to try to minimize the chances that he'll have any neurologic side effects."

Returning to normal life is "psychologically very empowering and it gives them a big boost and actually helps with the response to treatment," he said.

The mayor's office has said that Mr. O'Connor is being equipped with a laptop computer that can allow him to be a "virtual mayor," running the city from his hospital room or home.

The mayor has wrested his cell phone back from his wife, Judy, said Dr. Marks, "and it's going all the time."

It's certain that the cancer and chemotherapy will be a part of the mayor's life, and thus city government, for months, and maybe years.

That's because the disease could come back, even if the treatment clears the cancer cells from his spinal fluid and his brain scan returns to normal.

In Mr. O'Connor's situation, the cancer could recur in three or four years.

Some studies suggest that relapse is more likely in patients who, like the mayor, have lymphomatous meningitis, meaning there is cancer in the lining of the brain or spinal cord.

Neuro-oncologists aren't yet certain how to optimally treat it, "in part because none of the regimens have been compared head-to-head" in studies, Dr. Lieberman said.

Still, "with CNS lymphoma, relapse doesn't mean the patient is going to die," Dr. Lieberman noted. Often a relapse responds to the same drugs used the first time, or to different drugs.

City government last weathered a lengthy illness in 1987 and 1988, when Mayor Richard Caliguiri was diagnosed with and died from amyloidosis, a protein disorder.

Medically, central nervous system lymphoma and amyloidosis couldn't be more different. Politically, having a sick mayor changes things, said veterans of the Caliguiri years.

"The day-to-day mechanics of running the city" aren't affected by a mayor's illness, said George Jacoby, who was Mr. Caliguiri's executive secretary during his final years. "There's sort of an inertia to the place."

Personal diplomacy is tougher if the mayor is on a reduced schedule, he said. For instance, Mr. Caliguiri wanted to improve city relations with state government -- as Mr. O'Connor does -- but had limited ability to travel to the capital.

"The notion of taking on any new initiatives or major items that required the major's attention -- you had to think twice," said Jim Turner, who was Mr. Caliguiri's finance director.

He said that could be a bigger problem for Mr. O'Connor, falling ill in his seventh month in office, than for Mr. Caliguiri, who got sick during his 11th year there.

He said the half-year mark is a time when most administrations are settling on who should do what, and who should move on.

"Things are still shaking out, and I don't know how that shaking out will occur now."