"I feel fine, thanks," McCain told reporters as he and his wife, Cindy, left the Mayor Clinic in Scottsdale, Ariz., after 3 hours of tests and meetings with his doctors Thursday morning. He did not take questions before climbing behind the wheel of a black sport utility vehicle to drive home.

Once test results are available Friday, McCain's doctors will recommend a course of treatment, which the senator would begin Saturday, a McCain aide said. The treatment could include surgery.

The senator underwent blood work, a chest X-ray, electrocardiogram, echocardiogram, an MRI exam and a CT scan, his Washington office said. Those tests are to determine whether the cancer has spread and his general health.

The former Vietnam POW who fought a tough battle for the Republican presidential nomination initially was to have begun treatment on Monday, but the doctors recommended moving it up, said Ben Piscitelli, press secretary for Sen. Mike DeWine, citing McCain officials. DeWine, R-Ohio, is one of the four senators who supported McCain's presidential bid, and McCain had planned to campaign for him on Sunday, a trip he has canceled.

On learning Wednesday of the recurrence of McCain's melanoma, his former presidential rivals recalled the strength with which he had met past battles. "John is a good man and a fighter," said Republican nominee George W. Bush.

"He is so courageous he will ... just face it," said Democrat Al Gore.

"Both Senator McCain and Cindy have been heartened by the outpouring of love, affection and support that they have received from across the country," McCain spokesman Todd Harris said Thursday.

McCain's office announced Wednesday that doctors had found two spots of melanoma, on the senator's left arm and temple. McCain, 63, had another area of melanoma removed from his shoulder in 1993.

Friends said McCain has faithfully seen his doctor for checkups every three months since then. Melanoma that returns can be particularly difficult to treat.

Advisers said McCain didn't know whether the cancer had spread and was planning a news conference Friday to talk about his condition.

The treatments options depend on how deep the cancer is and whether it has spread. Melanoma near to the skin surface -- such as McCain's 1993 lesion -- can be surgically removed with excellent chances of recovery.

But the outlook is much worse once the cancer has expanded deeper than about two-tenths of an inch or spread into the lymph system or other tissues. That kind of cancer is so serious that patients are usually referred to experimental treatments of new anticancer drugs or vaccines that try to use the body's immune system to fight the disease.

Finding two areas of cancer simultaneously could suggest a more serious form of the disease.

Because McCain has had close medical scrutiny since his first bout with melanoma, the disease probably was caught early enough to be treatable, said Dr. Charles McDonald, past president of the American Cancer Society.

"He probably just has another melanoma," McDonald said. "Anybody who's had one, you have to keep very close eye on them. Nine times out of 10, they're going to develop another."

That's why McCain has been vigilant about getting checkups and using sunscreen, said Arizona Secretary of State Betsey Bayless, a McCain friend.

"If he had not been cautious about his health, there might be some concern. But because he is so good and so punctual in watching for it, (his family) is very upbeat about it," Bayless said.

McCain has canceled about a dozen upcoming campaign appearances with congressional candidates, advisers said, including a campaign stop Sunday for DeWine.

Those who have talked to McCain or his wife said he was upbeat.

"He has talked to lots of doctors, he has a very good sense of where he stands -- or at least he thinks he does," said Sen. John Kerry, D-Mass., who talked to Mrs. McCain on Wednesday. Kerry appeared on CNN's "Larry King Live."

"I can assure you he's in wonderful spirits. Beyond that, I can't tell you anything," said Deb Gullett, a former McCain staffer and longtime friend.

The news of McCain's cancer came on the third day of the Democratic National Convention and just days after he toured Western states with Bush, the victor in a spirited Republican campaign in which McCain won seven primaries.

The cancerous spot on McCain's temple -- dark purple and smaller than a dime -- had been apparent during McCain's visit to the Republican National Convention in Philadelphia two weeks ago. He had it removed Aug. 2 after returning to Washington in the midst of the convention -- a departure that had stirred some talk about hard feelings between Bush and McCain.

The Arizona senator returned to Philadelphia at Bush's invitation for the convention's final evening.

During his presidential campaign, McCain released hundreds of pages of medical records that detailed the lingering effects of injuries suffered during more than five years in a North Vietnamese prisoner of war camp.

Michael Ambrose, a POW center doctor made available by the McCain campaign in December 1999, said McCain and his fellow prisoners were kept in the Vietnamese sun for long periods, though it is impossible to link the cancer to his POW exposure.

"There's been a lot of talk about all the time he spent under the Vietnam sun," Bayless said. "Wherever the exposure was, it was overdone at some time in the past. But he's trying to preclude anything in the future."

After the December 1993 melanoma surgery, the records said, McCain regularly has had suspicious skin lesions or moles removed -- often basal cell carcinoma, the least aggressive and most common type of skin cancer.

The American Cancer Society estimates 47,700 Americans will be diagnosed with melanoma this year, and 7,700 will die.

The more sunburns, particularly early in life, the higher your risk. Fair-skinned people, consequently, are at highest risk. Also at high risk are people with more than 20 moles scattered around their body.