Possibly. Especially in non-smokers.
Given the number of people suffering from asthma, as well as the knowledge that lung cancer is the leading cause of cancer deaths in both men and women in the U.S., this is a very important question.
We don’t know the answer for sure, so what do we know?
Studies linking asthma to lung cancer
With regards to small cell lung cancer, studies in China do suggest a link between asthma and lung cancer that is significant. The increased risk varies in those studies, with people with asthma being 2 to 6 times more likely to develop lung cancer than those without asthma. It is important to remember that small cell lung cancer is a less common form of lung cancer, accounting for perhaps 15% of cases.Studies that look at lung cancer risk and asthma overall seem to suggest that the risk is greater in non-smokers than in smokers. A large review that looked at many studies found that, on average, lung cancer was 1.8 times more common in non-smokers with asthma than non-smokers who didn’t have asthma. When the studies looked at people overall in the U.S. -– including people who smoke –- the risk was that people with asthma were 1.4 times more likely to get lung cancer.
Why would asthma increase the risk of lung cancer?
One thought is that whatever causes contribute to asthma might contribute to lung cancer as well. We know that smoking or exposure to secondhand smoke can be a risk factor for asthma as well as lung cancer. Yet most of the studies that look at the link between asthma and lung cancer “control” for smoking. That is, they find a way to eliminate smoking as the link so they can look at other factors.Another theory is that long-term inflammation in the lungs due to asthma could be the underlying cause. Long-term inflammation has been evaluated recently as a cause of many cancers. Several studies suggest that chronic inflammation in the lungs due to asthma may be a "cofactor" in causing lung cancer –- meaning that asthma, combined with other causes, may work together to contribute to lung cancer risk.
But the jury is out. In one study, giving mice a chemical to cause lung cancer didn’t result in any more tumors in the mice with asthma. (In fact, having asthma didn’t seem to cause OR affect the progression of mice who already had lung cancer.). Likewise, a study out of Canada found that people with asthma had a lower risk of developing 8 types of cancer. It was felt in those studies that an “overactive” immune system, as seen with asthma, may actually help eliminate cells that could become cancerous.
What Should I Do if I Have Asthma?
What can you do if you have asthma? Certainly if you smoke, it is important to quit. Avoiding secondhand smoke is also important. But for non-smokers, it makes sense (though we don’t have any studies that prove it makes a difference) to make sure your asthma is as well-controlled as possible. After all, even if it doesn’t make a difference as far as lung cancer risk, living with asthma that is under control is simply a happier way to live.Further Reading:
Sources:
Brown, D. et al. Asthma and risk of death from lung cancer: NHANES II Mortality Study. The Journal of Asthma. 2005. 42(7):597-600.
Doris, K. et al. Allergic inflammation does not impact chemical-induced carcinogenesis in the lungs of mice. Respiratory Research. 2010. 11:118.
El-Zein, M. et al. History of asthma or eczema and cancer risk among men: a population-based case-control study in Montreal, Quebec, Canada. Annals of Allergy, Asthma & Immunology. 2010. 104(5):378-84.
Fan, Y. et al. Prior lung disease and lung cancer risk in an occupational-based cohort in Yunnan, China. Lung Cancer. 2011. 72(2):258-63.
Liang, H. et al. Risk of lung cancer following nonmalignant respiratory conditions among nonsmoking women living in Shenyang, Northeast China. Journal of Womens Health. 2009. 18(12):1989-95>
Lim, W. et al. Polymorphisms in inflammatory pathway genes, host factors and lung cancer risk in Chinese female never-smokers. Carcinogenesis. 2011. 32(4):522-9.
Santillan, A. et al. A meta-analysis of asthma and risk of lung cancer (United States). Cancer Causes & Control. 2003. 14(4):327-34.
Sanz, G. et al. Asthma and risk of lung cancer. Clinical and Translational Oncology. 2011. 13(10):728-30.
