Smokers with high levels of two chemicals in their urine were more likely than others in a study to get lung cancer, a finding that may lead to a new test to predict risk in time to prevent or treat the disease.
High levels of these chemical byproducts of tobacco smoke in the urine were linked to lung-cancer rates as much as 8.5 times higher than those of other smokers, said Jian-Min Yuan, the study leader and an associate professor of public health at the University of Minnesota in Minneapolis. He spoke in Denver today at the American Association for Cancer Research meeting.
Lung tumors are the most lethal form of cancer in the U.S., spurring 161,840 deaths and 215,020 new cases in 2008, according to the American Cancer Society, based in Atlanta. While there are about 60 possible carcinogens in tobacco smoke, pinpointing byproducts, or metabolites, that may spur the malignancies may help prevention, Yuan said.
"If we can identify a smoker with a high level of metabolites, and down the road they have a higher risk of lung cancer, public health workers can get them motivated to quit smoking," Yuan said in an April 16 telephone interview. "If they can't quit, we can do more intensive screening to find very small lung cancers that can be treated."
Yuan analyzed varying levels of metabolites in the urine of about 500 smokers drawn from the Shanghai Cohort Study and the Singapore Chinese Health Study, funded by the U.S. National Cancer Institute in Bethesda, Maryland. Dividing smokers into those having high, medium and low levels of the two chemicals, the researchers followed lung cancer diagnoses for 10 years.
Smokers with high levels of a byproduct called NNAL -- a known carcinogen in lab animals -- had twice the risk of getting lung cancer compared with smokers who had low levels.
People with high urine levels of cotinine, a nicotine byproduct, had three times the risk of those with low levels. Smokers with high levels of both NNAL and cotinine were 8.5 times more likely to get lung cancer than comparable smokers who had low levels of both chemicals.
The two chemicals appeared to be independent risk factors for lung cancer, even after adjusting for daily pack usage and the number of years of smoking reported by study participants, Yuan said.
The urine test isn't available for use by doctors, Yuan said. He predicted it will take three to five years to validate the test in ethnic groups around the world, refine the technology, and add other chemical carcinogens such as polycyclic aromatic hydrocarbons to the test panel.
How and why the chemical levels excreted in urine flag cancer vulnerability aren't known, Yuan said. "We are thinking smokers' uptake of the tobacco carcinogens is different," he explained. "Metabolic systems between smokers are different."
"I view this as the beginning point of developing prediction models," he added.
Margaret K. Offermann, deputy national vice president for research at the cancer society, said identifying patients with the chemical markers in their urine might help in "raising the red flag" in doctors' offices.