In both studies, lung cancer death rates were higher among men than women. In the CPS-I, the lung cancer death rate in men was nearly 19 per 100,000, but it was just 12 per 100,000 in women. That gap was narrower, but still statistically significant, in the CPS-II: 17 per 100,000 in men and 14 per 100,000 in women.
"Our findings are reassuring for women who've never smoked and who may have been alarmed by recent reports indicating their risk was higher than it actually is," said Thun, who is vice president of epidemiology and surveillance research at ACS.
Thun said there is a perception among many doctors that lung cancer is more common in non-smoking women because many of the non-smokers they see who have lung cancer are women. But that may simply be because there are 3 times as many women who have never smoked.
"Women didn't start smoking until later in the 20th century, so there are a lot more older women who've never smoked," he explained. "The risk of developing lung cancer -- like most solid tumors -- increases with age. It increases a lot faster if you're a current or former smoker, but it increases even if you've never smoked."
Lung Cancer Patients 'Shortchanged'
The issue of lung cancer in non-smokers was thrown into the spotlight earlier this year when Dana Reeve, widow of actor Christopher Reeve, died of the disease despite never having smoked. But active smoking isn't the only cause of lung cancer. People can also get this disease through exposure to secondhand smoke, asbestos, radon, and radiation therapy, among other causes.
In fact, about 10% -15% of all lung cancer deaths in the US -- between 17,000 to 26,000 each year -- are unrelated to active smoking. Of those, about 15,000 are in people who never smoked.
If all these cases of lung cancer were considered separately from smoking-related lung cancer, they would rank between 6 and 8 on the list of most common fatal cancers, Thun and his colleagues say. The study didn't find any evidence that lung cancer rates in non-smokers have changed substantially over the years.
Nevertheless, lung cancer still gets shortchanged when it comes to public attitudes and the search for cures, Thun said.
"The funding for lung cancer is small, given the burden of suffering and death that it causes, in part because of this unspoken assumption that blames the person for smoking," he said. "But the paper points out that lung cancer deaths due to factors other than smoking [constitute] a substantial burden. And then it gets shortchanged again because tobacco control gets underfunded below its contribution to suffering and death."
Differences in Whites, African-Americans
Thun's analysis also found racial differences in lung cancer deaths. African-American women who never smoked had significantly higher lung cancer death rates than white women who never smoked, and the gap got bigger between the first and second study. Rates were also higher among African-American men than white men, but there were too few black men in the first study to make the finding statistically meaningful.
Thun says these discoveries merit further research.
Lung cancer death rates have been higher among African-American men than white men since the 1960s, but most of this difference was thought to be due to different smoking patterns between the races. African-American men are a little more likely to be smokers, tend to smoke cigarettes with higher levels of tar, and tend to have higher levels of smoking-related chemicals in their blood.
The fact that this new analysis found a large difference in non-smokers, too, suggests there's more to the picture than just smoking habits.
"That is a novel finding that needs to be followed up," Thun said.
Citation: "Lung Cancer Death Rates in Lifelong Nonsmokers."Published in the May 17, 2006, Journal of the National Cancer Institute (Vol. 98, No. 10: 691-699). First author: Michael J. Thun, MD, American Cancer Society.
THE full impact of a drop in smoking rates is only just being felt, with sustained falls in deaths from cancer expected to improve as a generation of quitters move into middle and old age.
Experts describe the epidemic of tobacco smoking in terms of waves - the first wave is when rates of smoking rise and then reduce in response to public health messages about the dangers of tobacco.
The second wave - often with a two- to three-decade lag - is the rise in smoking-related deaths, followed by the corresponding fall as the benefits of quitting are realised, said the chief executive of the Cancer Institute NSW, Jim Bishop.
Rates of lung cancer, caused almost exclusively by smoking, have fallen 21 per cent for NSW men, but have increased by six per cent for women over the past 10 years - an indication of a peak in the number of women who took up smoking in the post-war years, Professor Bishop said.
Deaths from lung cancer have also fallen substantially in men - by 24 per cent - but have remained unchanged in women.
His comments are echoed in the latest edition of the journal Tobacco Control, where an editorial states: "Without reductions in smoking, there would have been virtually no reduction in overall cancer mortality in either men or women since the early 1990s. The pay-off from past investments in tobacco control has only just begun."
Even the most conservative estimate indicated that reductions in lung cancer, resulting from reductions in tobacco smoking over the past half century, accounted for about 40 per cent of the decrease in overall male cancer death rates in the US.
Reduced smoking rates prevented at least 146,000 lung cancer deaths in men in the US from 1991 to 2003, the editorial stated.
In NSW, there were 150 admissions to hospital each day from smoking-related illness, representing $1.7 billion in direct health costs each year, and $6.7 billion in indirect costs, such as lost work days and carers' costs, Professor Bishop said.
Half of all smokers in Australia will die of a smoking-related illness, one-third will die in middle age, losing an average of 22 years of life. But as soon as a smoker quits, their risk of heart attack and stroke drops immediately and there are other health benefits.
"As soon as you start to reduce the population at risk, you increase the benefit - if we accelerate the rates of quitting, we will see further reductions in cancer rates in the next decade," he said.
The chief executive officer of the NSW Cancer Council, Andrew Penman, said while lung cancer deaths were falling, more effort was needed to prevent further harm.
"How much death rates will fall depends on how much the Government is prepared to invest in terms of money and political capital in tobacco control."
With continuing strong anti-smoking campaigns, Dr Penman predicts the state's smoking rates could drop by one per cent each year over the next 10 years.
"If we want to go further than that and restrict access to tobacco products, you could bring it down much faster."
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Comment by Anne Martens
