LONDON - A respected international panel of experts says cellphones are possible cancer-causing agents, putting them in the same category as the pesticide DDT, gasoline engine exhaust and coffee.

The classification was issued Tuesday in Lyon, France, by the International Agency for Research on Cancer after a review of dozens of published studies. The agency is an arm of the World Health Organization and its assessment now goes to WHO and national health agencies for possible guidance on cellphone use.

Classifying agents as "possibly carcinogenic" doesn't mean they automatically cause cancer and some experts said the ruling shouldn't change people's cellphone habits.

"Anything is a possible carcinogen," said Donald Berry, a professor of biostatistics at the M.D. Anderson Cancer Center at the University of Texas. He was not linked to the WHO cancer group. "This is not something I worry about and it will not in any way change how I use my cellphone," he said _ from his cellphone.

After a week-long meeting, the expert panel said there was limited evidence cellphone use was linked to two types of brain tumors and inadequate evidence to draw conclusions for other cancers.

"We found some threads of evidence telling us how cancers might occur, but there were acknowledged gaps and uncertainties," said Jonathan Samet, the panel's chairman.

"The WHO's verdict means there is some evidence linking mobile phones to cancer but it is too weak to draw strong conclusions from," said Ed Yong, head of health information at Cancer Research UK "If such a link exists, it is unlikely to be a large one."

Last year, results of a large study found no clear link between cellphones and cancer. But some advocacy groups contend the study raised serious concerns because it showed a hint of a possible connection between very heavy phone use and glioma, a rare but often deadly form of brain tumor. However, the numbers in that subgroup weren't sufficient to make the case.

The study was controversial because it began with people who already had cancer and asked them to recall how often they used their cellphones more than a decade ago.

In about 30 other studies done in Europe, New Zealand and the US, patients with brain tumors have not reported using their cellphones more often than unaffected people.

Because cellphones are so popular, it may be impossible for experts to compare cellphone users who develop brain tumors with people who don't use the devices. According to a survey last year, the number of cellphone subscribers worldwide has hit 5 billion, or nearly three-quarters of the global population.

People's cellphone habits have also changed dramatically since the first studies began years ago and it's unclear if the results of previous research would still apply today.

Since many cancerous tumors take decades to develop, experts say it's impossible to conclude cellphones have no long-term health risks. The studies conducted so far haven't tracked people for longer than about a decade.

Cellphones send signals to nearby towers via radio frequency waves, a form of energy similar to FM radio waves and microwaves. But the radiation produced by cellphones cannot directly damage DNA and is different from stronger types of radiation like X-rays or ultraviolet light. At very high levels, radio frequency waves from cellphones can heat up body tissue, but that is not believed to damage human cells.

Some experts recommended people use a headset or earpiece if they are worried about the possible health dangers of cellphones. "If there is a risk, most of it goes away with a wireless earpiece," said Otis Brawley, chief medical officer of the American Cancer Society.

Brawley said people should focus on the real health hazards of cellphones. "Cellphones may cause brain tumors but they kill far more people through automobile accidents," he said. Brawley added it was also reasonable to limit children's use of cellphones since their brains are still developing.

Earlier this year, a US National Institutes of Health study found that cellphone use can speed up brain activity, but it is unknown whether that has any dangerous health effects.

In the US, the Food and Drug Administration and the Federal Communications Commission have found no evidence cellphones are linked to cancer.