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Smoking Goes From Bad to Worse, New Research Finds

Health: It's a deadlier carcinogen and causes more types of the disease than scientists believed.


Tobacco smoke is a much deadlier carcinogen and triggers a broader variety of cancers than researchers had previously believed, according to the most comprehensive study of smoking ever undertaken.

The new study also provides the first definitive evidence that secondhand smoke causes lung cancer, increasing the risk to those people exposed by about 20%. The new study firmly links smoking to stomach, liver, cervical and kidney cancer, as well as to myeloid leukemia. Such links were suspected, but not proved.

"We are still learning just how damaging cigarette smoking is," Dr. Jonathan Samet of the Johns Hopkins School of Public Health told a London news conference Wednesday. "Only now are we beginning to see the full picture of what happens when a generation begins to smoke at an early age ... the full picture is more disturbing than what we saw when we only had the smaller pieces."

Samet chaired an international panel of 29 experts convened by the United Nations' International Agency for Research on Cancer to conduct the first comprehensive evaluation of smoking research since 1986. The team examined more than 3,000 studies involving millions of smokers. Their report will be published later this year, but parts of it are scheduled to be posted on the agency's Web

"When we put all that information together, the picture becomes much clearer," said Dr. Patricia A. Buffler of UC Berkeley, a member of the research group. "This confirms many things that people were concerned about."

An estimated 1.2 billion people worldwide smoke, and their prognosis is grim, according to the study. At least half of them will be killed prematurely by smoking-related diseases, including cancer, heart disease and emphysema. Half of those deaths will occur in middle age, with an average loss of 20 to 25 years of life expectancy.

In addition to finding new links, researchers concluded that the risks for some tumors previously linked to smoking was higher than suspected.

For tumors of the bladder and kidney, for example, researchers had previously thought smokers had three to four times the normal risk. The new data indicate the actual risk is five to six times normal, IARC director Dr. Paul Kleihuis said.

Some of the cancers are associated with other factors as well. Cervical cancer is associated with the human papilloma virus, stomach cancer with the bacterium Helicobacter pylori, and liver cancer with hepatitis viruses. But in each of those cases, Buffler said, smoking doubles the risk.

The study, which Buffler said was the most comprehensive ever undertaken, found no evidence, however, that smoking increases the risk of prostate, breast or endometrial cancers. That is probably because these tumors are triggered primarily by hormones rather than by exposure to chemicals in the environment, said Sir Richard Doll of Oxford University, a member of the panel.

The team also looked at more than 50 studies focused on exposure to secondhand smoke and concluded that such exposure is linked to lung cancer, but no others. "It is a very strong association," Buffler said. There are more than 4,000 chemicals in cigarette smoke and new studies have shown that they can be measured in the body fluids and urine of nonsmokers.

"It is now well established that they are being breathed in by nonsmokers, absorbed, and are having an impact on genetic material," Buffler said.

Some national agencies, including the U.S. Environmental Protection Agency and the National Cancer Institute, had concluded that secondhand smoke causes cancer, but this is the first time an international group like the U.N. has reached the same conclusion.

The study also pointed to some disturbing trends, such as the marked increase in the number of women smoking and the growing incidence of smoking in developing countries.

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