Does Asthma Raise the Risk of Lung Cancer?

Are People with Asthma More Likely to Get Lung Cancer?

asthmatic man using a steroid inhaler that may reduce lung cancer risk
Do people with asthma have a higher risk of lung cancer?. istockphoto.com

Asthma may be a significant risk factor for lung cancer in both smokers and never smokers, with lung cancer being roughly 40% more common in people who have asthma that requires treatment. The risk, however, varies with lung cancer types, and the risk appears to be less with lung adenocarcinoma, the type of lung cancer most often seen in never smokers, women, and young adults. Research looking at the underlying biology is young, yet it appears that controlling asthma may, in some cases, reduce the risk of lung cancer. Learn about the correlation between asthma and lung cancer, some possible explanations for the connection, and what you can do if you're living with asthma today.

Asthma and 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

Several studies have looked at the association between asthma and lung cancer in the past, with mostly inconclusive results. Yet recent analyses of these studies are beginning to make the picture clearer.

A 2017 meta-analysis of studies, found that asthma was significantly associated with an increased risk of lung cancer, with those who have asthma being 44% more likely to develop lung cancer. This was true for both Caucasians and Asians, men and women, and smokers and non-smokers. The risk, however, was not seen with lung adenocarcinoma.

Lung adenocarcinoma is the type of non-small cell lung cancer that is found most commonly among never smokers, women, and young adults with lung cancer.

A large 2019 study also looked at the association of cancer, asthma, and allergies. There was a positive association between lung cancer and smoking, with asthma associated with a 25% increased risk of lung cancer. There was no association between asthma and breast cancer or prostate cancer. Allergies, in contrast, were associated with a 20% reduced risk of lung cancer, though no association was seen between allergies and breast or prostate cancer.

Never Smokers with Asthma and Lung Cancer Risk

Some studies have found the association greater among non-smokers with lung cancer. A large UK study (1.2 million people) found that never smokers who had asthma (asthma severe enough to require treatment) were 32% more likely to develop lung cancer.

Types of Lung Cancer and Asthma

As noted, a large meta-analysis of studies did not find asthma to be linked with lung adenocarcinoma. This was surprising given that asthma may be a greater risk factor in never smokers, and lung adenocarcinoma is by far the most common type of lung cancer in never smokers. One systematic investigation by the International Lung Cancer Consortium broke the link between asthma and lung cancer down by cancer type. They found the strongest links between asthma and squamous cell carcinoma of the lungs (69% increase), and small cell lung cancer (71% increase), and a weaker link between asthma and lung adenocarcinoma (9% increased risk).

Correlation vs. Causation

One question that has been raise is whether the connection between asthma and lung cancer may be correlation alone and not causation. The difference between correlation and causation is a common concern in medicine. For example, there is a strong correlation between eating ice cream and drowning, but this does not mean that eating ice cream causes drownings. In the International Lung Cancer Consortium study above, the risk for lung cancer was strongest in the first two years after an asthma diagnosis suggesting that the link was not causative. In fact, it's been hypothesized in this setting that asthma could actually be an early symptom of lung cancer that was not yet diagnosed.

Common Risk Factors

Another potential explanation for the link between asthma and lung cancer is common risk factors. In the ice cream example, this would be looking upstream for commonalities, such as eating ice cream and drowning both taking place in the summer. 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 (these are called "controlled studies"). When this is done, the risk of lung cancer associated with asthma still remains.

Reducing One Factor to Look for a Change in the Other

Another way to evaluate whether a link is correlation or causation is to evaluate the response when one factor is decreased. For example, could reducing or eliminating ice cream intake reduce the risk of drowning? In this case, could reducing asthma inflammation reduce the risk of lung cancer? There is some evidence that is discussed below.

Further Studies of Links

Another way to evaluate a correlation is to see whether there is some reason why a factor (such as eating ice cream) would cause drowning. It appears that there are some biological reasons why asthma might raise lung cancer risk.

There are, however, mechanisms by which asthma might raise the risk of lung cancer.

Mechanisms

When there is a question as to correlation and causation, researchers often attempt to see if their is an underlying mechanism that would explain causation.

Inflammation

One theory is that long-term inflammation in the lungs due to asthma could be the underlying cause of lung cancer. 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. One of these "other" factors may include a genetic predisposition (genetic polymorphisms), and we are learning that genetics appears to play an important role in lung cancer in never smokers.

Biological Evidence

We are learning that cancer is not just an errant clone of cells that grows alone. Rather, cancer cells interact very closely with nearby tissues, and area that has been coined the "tumor microenvironment."

In asthma, a type of connective tissue cells known as bronchial fibroblasts are important. In the lab, researchers look at lung cancer cells and signals secreted by human bronchial fibroblasts from both people with and without asthma. The lung cancer cells exposed to signals from fibroblasts from people with asthma were more motile. It's not certain whether this study could translate to what happens in the human body, and if so, if it would only affect lung cancer cells already present, but the study does illustrate how evaluation of the underlying biological processes in place might better help explain any connection between asthma and lung cancer in the future.

That said, other factors, such as exposure to carcinogens, may play less of a role. A study in mice suggested that asthma did not have an impact on chemical-induced carcinogenesis in mice (cancer caused by DNA damage from cancer-causing substances in the environment such as tobacco smoke and asbestos). The jury is out, however, as it's not certain if the fact that giving mice a chemical to cause cancer didn't result in any more tumors in mice translates to humans exposed to carcinogens in the environment.

Reducing Lung Cancer Risk with Asthma

The question above, about whether improving control of asthma may lower lung cancer risk, is important from both a standpoint of defining whether asthma has a causative role, and if so, reducing the risk of lung cancer in people with asthma.

Inhaled Corticosteroids, Asthma, and Lung Cancer Risk

A Nationwide study of over 37,000 people with asthma suggests that controlling inflammation with the disease may indeed lower lung cancer risk.

In this 2018 study, it was found that people with asthma who used inhaled corticosteroids on a regular basis were, on average, 58% less likely to develop lung cancer.

In this 2018 study, it was found that people with asthma who used inhaled corticosteroids on a regular basis were, on average, 58% less likely to develop lung cancer.

Certainly, this potential benefit of inhaled corticosteroids needs to be weighed against the risks and side effects of steroid inhalers, such as easy bruising and more. Whether or not controlling your asthma makes a significant difference, however, is only one concern. Even if these inhalers don't make a difference with regard to lung cancer risk, living with asthma that is under control is simply a happier way to live.

If You Have Asthma

If you have asthma and are worried about the potential risk of lung cancer, there are several things you can do to lower your risk.

  • Don't smoke
  • Check your home for radon (according to the EPA, radon is the leading cause of lung cancer in non-smokers, and it's very easy to test your home and eliminate radon if found)
  • Avoid secondhand smoke
  • Practice caution (read labels and heed them) with chemicals you are exposed to at work and at home
  • Know your risk factors
  • Undergo CT lung cancer screening if you quality

Check out our tips on preventing lung cancer (some may surprise you) and remember: Anyone who has lungs can get lung cancer.

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Article Sources

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