Cockpit Crews at Increased Risk of Leukemia

From the WebMD Archives

Dec. 9, 1999 (Atlanta) -- High-flying jet pilots could be at higher risk of developing one form of leukemia, according to a study from the Dec. 11 issue of the journal TheLancet. But it's those long, post-flight hours spent lying on sunny beaches that are likely causing the many skin cancer cases found in this group.

And for frequent-flyer passengers -- who often log thousands of air hours every year -- it's fuel to analyze their own cancer risks, says one oncologist.

"Our study showed increased risks of acute myeloid leukemia [cancer of the blood] and total cancer among Danish male jet cockpit crew members flying more than 5,000 hours," says Maryanne Gundestrup of the Danish Cancer Society and lead author of the study. "This finding could be related to cosmic radiation, in as much as the risk is seen in the most exposed group -- those flying high for many hours."

During flights, crews are exposed to naturally occurring cosmic radiation, with the dose doubling for every mile increase in altitude, the report says. A flight crew may get four-to-five times the natural background radiation that reaches ground level. However, of greater concern to the authors is exposure to neutron radiation, which damages surface cells, causing skin cancer.

"Both malignant melanoma and [other] skin cancer were found in excess in cockpit crews with a long flying history, probably attributable to sun exposure during leisure time at holiday destinations," adds Gundestrup.

This was the first comprehensive study that includes all commercially licensed, cockpit crewmembers in one country. The researchers analyzed records dating back to 1946 from aviation clinics, the Danish Cancer Registry, and a population registry. The aim was to study whether an increased cancer risk could be shown, and if the risk could be attributed to cosmic radiation -- based on both flying hours and aircraft (which would indicate how high the craft was flying).

"This study adds to previous literature, showing that prolonged flying does increase exposure to cosmic radiation. The authors describe the results as 'reassuring,' that even this highly exposed group did not show a major increase in cancer risk, although there was an increased risk of acute myelogenous leukemia," Michael Thun, MD, who heads epidemiological research at the American Cancer Society, tells WebMD in an interview. "The incidence of melanomas was not reassuring. The patterns of skin cancers were clearly on chest and arms, areas that would be covered by clothing in the aircraft. The pattern of those skin cancers was due to sun exposure at their destination."

Melanoma, the most lethal form of skin cancer, is expected to be diagnosed in 44,000 people in the U.S. by end of 1999, says Thun.

Trust the data in this study, Craig Silverman, MD, associate professor of radiation oncology at Temple University School of Medicine, tells WebMD. With their socialist health system, Scandinavian countries have an advantage in epidemiological studies like this. "It's very good, very clean data."

"It confirms what we continue to believe ... that there are risks when flying in aircraft, risks that the general public does not appreciate. It's our policy [at Temple] to warn parents of newborns against flying, and that exposure you get from New York to L.A. is the equivalent of several chest X-rays."

Radiation exposure -- and the sun's strength at high altitudes -- is vastly underestimated, says Silverman. "Because of thinner atmosphere, you are indeed exposed to more sun rays and have less protection. When you're in the mountains and skiing, you can get a pretty bad sunburn and not recognize why."