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Lung Cancer Rates Among Nonsmokers Not on the Rise

International study debunks some commonly held beliefs about this type of cancer

TUESDAY, Sept. 9, 2008 (HealthDay News) -- The most comprehensive global snapshot ever taken of lung cancer diagnoses and related death rates among patients who have never smoked has found that, contrary to prior indications, lung cancer risk is not on the rise.

The analysis also revealed that the lung cancer death rate among those who have never smoked is higher among men than women.

Both findings stem from an enormous collaborative international effort that draws on information from 13 large studies and 22 cancer registries, and represents upwards of 2 million men and women living in 10 countries across North America, Europe, Asia, the Middle East and Africa.

"The great majority of lung cancers are caused by smoking," stressed study author Dr. Michael Thun, head of epidemiological research at the American Cancer Society. "But there has been a lot of interest lately in those lung cancer cases that affect patients who have never smoked, in part because of prominent nonsmoking patients who have had the disease in recent years, like Dana Reeve," who died from the disease at the age of 44 in 2006.

"This increased interest has led to a lot of concern, misperceptions and misconceptions regarding the state of risk and susceptibility," Thun added. "So, this work addresses this speculation, firstly by finding that, over the last 50 to 70 years, there has been no increase in lung cancer among people who have never smoked. And secondly, that the popular belief that 'never-smoked' women are more likely to develop the disease than men turns out not to be the case. And thirdly, that African-Americans have a higher death rate than whites."

Thun and his colleagues collectively published their observations in the September issue of PloS Medicine.

Their conclusions are based on incident and mortality rates for lung cancer among more than 630,000 and 1.8 million men and women (respectively) who had never smoked, and who had participated in one of 13 different large studies (each involving a minimum of 20,000 participants) conducted in North America, Europe or Asia.

The authors also reviewed cancer registry statistics specifically regarding women that had been compiled some time between 1983 and 1989 in 10 countries (across Asia, Africa, Europe, the Middle East, China and India). In all these places, the rate of smoking among women was known to be relatively low.

After digesting these and other variables, Thun and his associates concluded that since the 1930s, there has been little to no change in either lung cancer incident or death rates among lifelong non-smoking American men and women.

The research team further determined that lung cancer death rates are higher in men who never smoked than women, and that this apparent "mortality gap" appears to widen as people age.

However, in terms of lung cancer incidence among this group, the rate among women outstripped that of men for those under the age of 70, particularly among women between the ages of 50 and 59. Yet that dynamic reversed after age 80, when more men begin to be diagnosed with the disease.

Nonsmoking black men and women were found to have a higher death rate from the disease than those of European descent, while black women also appeared to have a higher incidence rate as well. No conclusion could be drawn regarding incidence among black men.

Lung cancer incidence was also observed to be two to three times higher among Asian women living in East Asia (Philippines, Hong Kong, Japan, and Singapore) as compared with women living in Western countries with similarly low female smoking rates. And overall, Asian men and women living in Asia (but not those of Asian descent living in the United States) appear to face a higher lung cancer death rate than people of European descent.

Thun noted that 85 percent to 90 percent of lung cancer cases are caused by smoking, which translates into roughly 1.4 million lung cancer deaths across the globe each year.

Nevertheless, he pointed out that the pool of remaining patients who develop the disease due to other factors is a public health issue that is worthy of investigation.

"We're talking about figures that are right up there with brain cancer in terms of the hard numbers of patients," he noted. "And relative to other cancers, lung cancer research is under-funded. So, the value of this kind of broad effort to better understand the problem is immense."

Dr. Neil Schachter, a professor of pulmonary medicine at Mount Sinai Medical Center in New York City, agreed that the current analysis addresses an important issue, given that the number of nonsmoking lung cancer patients is "small, but obviously significant".

"But though the findings are not that surprising and certainly form an impressive observation, this work needs to be followed up," Schachter cautioned. "For example, with respect to men having a higher death rate, it is important to recognize that men may have more co-morbidities than women. That is, they have more associated diseases. And the fact you have associated diseases may make you more prone to dying from the complications of lung disease. So, there are a lot of factors to consider before coming to any strong conclusions."

More information

For more about lung cancer and risk factors, visit the American Cancer Society.

SOURCES: Michael Thun, M.D., head, epidemiological research, American Cancer Society, Atlanta; Neil Schachter, professor, pulmonary medicine, Mount Sinai Medical Center, New York City; September 2008, PloS Medicine
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