By Alicia Chang The Associated Press

LOS ANGELES – Blacks who smoke up to a pack a day are far more likely than whites who smoke similar amounts to develop lung cancer, suggesting genes may help explain the racial differences long seen in the disease, researchers say.

The largest study ever done on the subject also found that Hispanic and Asian smokers were less likely than black smokers to develop the disease – at least up to a point. The racial differences disappeared among heavy smokers, or those who puffed more than a pack and a half per day.

Doctors have long known that blacks are substantially more likely than whites to develop lung cancer and more likely to die from it. But the reasons for the disparity are unclear.

Some say the difference is a matter of genetics, while others contend smoking habits may play a role. For example, researchers say blacks tend to puff more deeply than whites, which may expose them to more carcinogens. Smoking rates are also slightly higher among blacks, but whites tend to smoke more cigarettes a day.

In the latest study – published in Thursday’s New England Journal of Medicine – researchers compared the lung cancer risk among ethnic groups who smoked the same amount.

While the study did not address the possible reasons for the racial disparity, lead researcher Christopher Haiman, an assistant professor of preventive medicine at the University of Southern California, said the findings suggest genes may be one of the factors that explain the phenomenon.

The study involved more than 180,000 people, more than half of them minorities. Patients filled out questionnaires about their smoking habits, diet and other personal information.

Researchers from USC and the University of Hawaii analyzed lung cancer cases over an eight-year period. After adjusting for diet, education and other factors, the researchers found that whites who smoked up to a pack a day had a 43 percent to 55 percent lower risk of lung cancer than blacks who smoked the same amount. Hispanics and Japanese-Americans were 60 percent to 80 percent less likely than blacks to develop the disease.

The study found no difference in lung cancer risk among the various ethnic groups for those who smoked more than three packs a day.

Black, Hispanic and Japanese-American men who never smoked had higher risks of lung cancer than white men, but hardly any difference was seen in women in the same ethnic groups.

According to the American Lung Association, black men are 50 percent more likely to develop lung cancer and 36 percent more likely to die from the disease than white men.