Does Asthma Raise the Risk of Lung Cancer?

Are People with Asthma More Likely to Get Lung Cancer?

asthmatic man using an inhaler
Do people with asthma have a higher risk of lung cancer?.

Does Asthma Raise the Risk of Lung Cancer?

Asthma may raise the risk of lung cancer although we are just starting to see the link and how common it may be.  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. Overall, it appears that the correlation is strongest in never smokers. What have we learned so far?

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 percent 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.  A more recent study found that asthma is associated with an increased risk of all the major subtypes of lung cancer including small cell lung cancer as noted earlier, and non-small cell lung cancers including lung adenocarcinoma, squamous cell carcinoma of the lungs, and large cell lung cancer.

Why would asthma increase the risk of lung cancer?

One thought is that whatever factors contribute to the development of 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 (called controlled studies.) When this is done, the risk of lung cancer associated with asthma still remains.

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.

Yet another thought is that there is an underlying process in addition to inflammation that may increase risk. We know that having COPD is a direct risk factor for lung cancer as well. In other words, people with COPD are more likely to get lung cancer than would be predicted based on their smoking history alone.

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.

Lung cancer is a devastating disease and is now the leading cause of cancer deaths in both men and women in the United States. Lung cancer in never smokers is the 6th leading cause of cancer deaths overall. Check out these tips on preventing lung cancer - some you may be very familiar with, and some that may surprise you.  And remember: anyone with lungs can get lung cancer.

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