When it comes to lung cancer rates among smokers, scientists say race and ethnicity matter. A new study reports significant differences in the rates among smokers from five U.S. ethnic and racial groups, with the highest among blacks and native Hawaiians.
The incidence of lung cancer in the United States is highest among blacks and Polynesians and lowest among Japanese-Americans and Hispanics, with whites in between. Some people have thought that differences in smoking behavior might account for this disparity. But a study in the New England Journal of Medicine shows that these relative disease rates remain even when the number of cigarettes smoked is comparable.
Researchers from the Universities of Southern California and Hawaii examined lung cancer rates among 184,000 American men and women of European, African, Japanese, Hispanic ancestry and native Hawaiians. Their average age was 60.
They found that of those who smoked 20 or fewer cigarettes a day, the blacks and native Hawaiians had the greatest risk of lung cancer. Whites had about half the risk of these two groups, while Japanese-Americans and Hispanics had one-fifth to two-fifths the risk respectively.
The reason why is a mystery.
"The factors that explain these differences we don't know about," says Christopher Haiman of the University of Southern California and lead author of the study.
He adds that differences in lung cancer risk among racial and ethnic groups cannot be explained by diet, occupation, socioeconomic status or other known or suspected factors. He suggests one reason might be genetic differences in how their bodies process the cancer-causing chemicals in tobacco.
"There could be variation in how different populations metabolize nicotine, which could influence smoking behaviors such as the intensity of smoking, the depth and frequency of inhalation, and therefore influence the uptake of carcinogens," he notes. "We know there are genes that are shared across populations, but they have different frequencies which could make some populations more susceptible to the effects of tobacco smoke. But it's most likely due to combinations of unmeasured environmental factors as well as genetic differences."
The research shows that racial and ethnic differences in lung cancer risk disappeared among heavy smokers in the study. Their chance of getting the disease was similar if they smoked 30 or more cigarettes a day.
Whether the findings can be applied directly to ancestral populations in Africa, Europe, and Japan is unclear. American racial groups are a blend of genetic heritages. According to one expert on disease distribution among populations, Neil Risch of the University of California at San Francisco, black Americans average about 20 percent European ancestry. U.S. Hispanics are even more complex, tracing their lineage to Europe, the Americas, and Africa.
"We have somewhat different groups here than internationally in terms of the ethnic makeup of the United States," says Mr. Risch.
But Risch says from the policymaking point of view, the ethnic and racial differences in lung cancer are unimportant.
"From the public health perspective, these findings don't really matter, because it shows that the ethnic differences pretty much disappear when you eliminate smoking," he explains. "So from the perspective of public health, it may not be that helpful."
But both Risch and study author Christopher Haiman say such findings could be useful for the information they might provide about the mechanisms by which cancer causing compounds influence the risk of disease.