PORTLAND, Ore. -- The same Oregon court that slapped Big Tobacco with a huge punitive damages award has handed the industry a victory by rejecting a class-action lawsuit for medical monitoring costs.

The Oregon Supreme Court ruled unanimously Thursday that smokers must show actual harm to make a negligence claim against cigarette manufacturers -- not the mere possibility of harm in the future.

The lawsuit by Patricia Lowe on behalf of about 400,000 Oregonians argued the tobacco companies were negligent because they "knew or should have known that their cigarettes contained toxic and hazardous substances likely to cause lung cancer."

Lowe argued the industry should pay for screening tests such as spiral CT scans, a three-dimensional form of computerized X-rays that can detect lung tumors at their earliest and most treatable stage.

The court said that Oregon law has long recognized that "a threat of future physical harm is not sufficient."

James Coon, the attorney for Lowe, said the ruling shows the law still is trailing behind science.

"Certain toxic products put people at risk for future injury," Coon said, but "medical monitoring is a concept that ancient common law has trouble dealing with, and the court in this case applied old common law concepts without flexing them in any way."

Carl Tobias, a University of Richmond law professor who specializes in torts, or damage claims, agreed.

"It doesn't fit in the box of traditional tort law," Tobias said. "Tort law by definition is after the fact. It aims primarily to compensate for past harm -- not to prevent future harm."

But Tobias noted that Justice Martha Lee Walters, in a concurring opinion, left open the possibility the law could change "when science and medicine are able to identify harm before it becomes manifest."

Such techniques may be coming soon, said Thomas Glynn, spokesman for the American Cancer Society in Washington, D.C.

"We're probably about two years away before we can say whether we can detect lesions early enough to know what the effect will be," Glynn said.

Ben Zipursky, a Fordham Law School professor who specializes in product liability, said it was ironic the ruling came from the same court that recently affirmed a nearly $80 million punitive damages award against tobacco giant Philip Morris after it was struck down by the U.S. Supreme Court.

"This is the very court that has most aggressively ruled against Philip Morris," Zipursky said.

But the ruling was similar to most state courts around the nation in similar cases, despite a move toward loosening up the definition of actual harm, he said.

"This case is important because it didn't go the extra step," Zipursky said. "And it's not surprising there' a limit to how far they're going to push."

Philip Morris officials said they were pleased with the ruling.

"This decision confirms that Oregon law -- like the law of many other states -- refuses to allow claims for medical monitoring by those who have no current injuries," said Murray Garnick, senior vice president and associate general counsel for Altria Client Services on behalf of Philip Morris.

R.J. Reynolds Tobacco Co., one of the other five companies named in the lawsuit, welcomed the ruling in a statement released Thursday.

The other companies were Brown & Williamson Tobacco Corp., Lorillard Tobacco Co. and Liggett Group Inc.