Smoking is cause of even more cancers, study shows

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

The study also provides the first definitive evidence that secondhand smoke causes lung cancer, increasing the risk by about 20 percent. It firmly links smoking to stomach, liver, cervical, nasal sinus, uterine 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 yesterday. "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."

New perils A comprehensive study says that in addition to lung cancer, these cancers are now firmly attributed to tobacco smoke: • uterus • stomach • liver • cervix • kidney • myeloid leukemia • nasal sinus No longer considered linked to smoke are cancers of the: • breast • endometrium (womb lining) • prostate

Samet chaired a panel of 29 experts from 12 countries convened by the United Nations' International Agency for Research on Cancer (IARC) 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 this year, but parts of it are to be posted on the agency's Web site (www.iarc.fr) today.

"When we put all that information together, the picture becomes much clearer," said Dr. Patricia Buffler of the University of California, 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 risks for some tumors previously linked to smoking were higher than suspected.

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

Some 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. Smoking doubles the risk in each of those cases, Buffler said.

The study found no evidence, however, that smoking increases the risk of prostate, breast or endometrial cancers. That probably is 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 on secondhand smoke and concluded such exposure is linked to lung cancer, increasing risk by 20 percent, but to 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," she said.

Some national agencies, including the Environmental Protection Agency and the National Cancer Institute, had concluded previously that secondhand smoke causes cancer. This is the first time an international group such as the United Nations has reached the same conclusion.

The group found no clear evidence that children exposed to their parent's tobacco smoke in the womb or after birth have an elevated risk of developing childhood cancers. Whether they face an increased risk of cancer in adulthood remains unclear, the panel said.

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.

"Some people had thought that women might have lower risks, but that is not true," Buffler said. "If their exposure to tobacco smoke is comparable to that of males, their risks are comparable to those of males."

The group also came out strongly for efforts aimed toward smoking cessation.

"We were impressed to see that stopping smoking at any age results in a marked benefit to the smoker," Buffler said. "Even stopping at age 50 would reduce full lifetime risks. The risk never returns to that of a nonsmoker, but there is a marked impact on mortality."

Information from The Associated Press is included in this report.