A new study of nearly 1,500 people with pancreatic cancer confirms that cigarette smoking boosts the risk of the disease.

The study also found that, given an equal total exposure to smoking, a person who smoked less for a longer period of time would be at greater risk of pancreatic cancer than someone who smoked more for a shorter period of time.

Smoking is a known risk factor for pancreatic cancer. To better understand how patterns of exposure to cigarettes may relate to disease risk, Dr. Shannon M. Lynch, of the National Cancer Institute in Bethesda, Maryland, and her colleagues analyzed data for 1,481 people with the disease and 1,539 healthy controls from the International Pancreatic Cancer Cohort Consortium.

Overall, the researchers found, smokers were 1.77 times more likely than people who had never smoked to develop pancreatic cancer.

Risk rose steadily with the amount of cigarettes a person smoked daily, the length of time that they smoked, and the total “smoking dose” - or the number of packs a person smoked daily and the number of years they smoked.

People who had quit smoking 10 years previously were still at increased risk of pancreatic cancer, while the risk for people who had quit for 15 years was similar to that of people who had never smoked, the researchers report in the American Journal of Epidemiology.

As the number of “pack-years” increased, excess risk declined with the intensity of smoking exposure, “suggesting greater risk for a total exposure delivered at lower intensity than for an equivalent exposure delivered at high intensity,” Lynch and her colleagues write.

Similar risk patterns have been seen for lung cancer, bladder cancer, cancer of the oral cavity, kidney cancer, and esophageal cancer, they add, which suggests that smoking may increase the risk of all of these cancer types through similar mechanisms.

The current analysis found 15% of all pancreatic cases were due to cigarette smoking. “Because smoking is an established pancreatic cancer risk factor, smoking cessation continues to be an effective strategy for decreasing the burden of this disease,” the investigators conclude.

Pancreatic cancer is the fourth-leading cause of death due to the cancer in the US, with fewer than 5% of people surviving for five years after being diagnosed with the disease.

Pancreatic cancer is particularly deadly because there is no way to screen for it, so people are often diagnosed late.

SOURCE: American Journal of Epidemiology, August 15, 2009.