Smoke Tracks

For some racial and ethnic groups, even smoking fewer cigarettes can mean more lung cancer.

by Lori Oliwenstein

Smoking kills. Make no mistake about it. No one is immune to the carcinogenic effects of cigarette smoke. No matter what your heritage, if you smoke the risk of lung cancer and other diseases rises significantly.

But a recent study by scientists from the Keck School of Medicine of USC and the University of Hawaii in Honolulu showed there are differences in the risk of developing lung cancer among racial and ethnic populations. The differences were most pronounced among people who smoke fewer than a pack-and-a-half, or 30 cigarettes, per day.

Backing up this conclusion are data published in the January 25, 2006 issue of the New England Journal of Medicine. Specifically, the researchers found that lung cancer is more likely to develop in moderate cigarette smokers who are African American or Native Hawaiian than in smokers who are white, Japanese American or Latino. The study was supported by a grant from the National Cancer Institute.

In the study, the research team analyzed the incidence of lung cancer among 183,813 African-American, Japanese-American, Latino, Native Hawaiian and white men and women from a prospective Multiethnic Cohort Study of more than 215,000 individuals in California and Hawaii. These individuals were followed for as many as eight years, from their entry into the study (some time between 1993 and 1996) and the study’s end point in 2001.

Between 80 and 90 percent of lung cancer cases can be attributed to cigarette smoking. Previous research had shown that there were disparities in the distribution of lung cancer risk, with African-American and Native Hawaiian smokers seeming to be more likely to get lung cancer than other racial and ethnic populations.

“We wanted to see to what extent population-based differences in lung cancer incidence can be explained by differences in cigarette smoking,” says Christopher Haiman, Sc.D., assistant professor of preventive medicine at the Keck School and the lead author on the study. “This is the largest study to date to address this question.”

Statistics on smoking have shown that the habits of smokers vary widely among racial and ethnic populations. For instance, although 30.1 percent of African Americans and 27.3 percent of whites currently smoke, only 8 percent of African-American smokers smoke more than 25 cigarettes a day, as compared with 28 percent of white smokers. In other words, African Americans are much less likely to be heavy smokers than white smokers.

In the New England Journal analysis, 1,979 lung cancer cases from the Multiethnic Cohort were identified prospectively over the period between baseline (1993-1996) and 2001. The cases were identified by linkage to the Surveillance, Epidemiology and End Results (SEER) cancer registries for Hawaii and California, with deaths being identified by death certificate files in both states, and through the National Death Index.

What they found was that the risk of smoking-related lung cancer among those who smoked less than a pack-and-a-half a day not only varied by ethnicity, but by how many cigarettes the individuals in the study smoked each day—the so-called smoking “dose.”

• Among those who smoked fewer than 30 cigarettes per day, the risks for lung cancer among African Americans and Native Hawaiians were significantly greater than for the other groups in the study.

• Among those who smoked fewer than 10, or between 11 and 20 cigarettes per day, relative risks of lung cancer for Japanese Americans and Latinos ranged from .21 to .39 and for whites .45 to .57 compared with African Americans, whereas the risks for Native Hawaiians and African Americans were similar.

• At levels above 30 cigarettes per day, the cancer risk differences between populations were not significant.

• The environmental measures looked at in this study—occupation, diet and education—could not explain what Haiman calls “the striking racial and ethnic differences in the risk of lung cancer associated with cigarette smoking.”

Why would lung cancer risk fluctuate between racial and ethnic populations?

“We were not able to determine the reason for these differences in this study,” Haiman says. “But the data do suggest that differences in susceptibility may exist, which may be due to differences in the metabolism of nicotine or tobacco carcinogens among the various groups, or perhaps non-genetic factors that vary in frequency across populations.”

Haiman cautions, however, that these findings should not change the overall public health message. “The truth is still that the elimination of smoking—in any and all ethnicities—will dramatically reduce lung cancer incidence.”

The results of the study reinforce what has been increasingly clear for many years: Smoking, even at a relatively low level of a few cigarettes each day, raises the risk of lung cancer. And other studies have shown that smoking leads to higher risk of heart disease as well as other diseases, such as emphysema.

The simple answers to reducing the risk of contracting diseases caused by smoking remain the same: Don’t smoke. And if you already smoke, quit.