Does Asthma Raise the Risk of Lung Cancer?

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.

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, 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.

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).

Common Risk Factors

Another potential explanation for the link between asthma and lung cancer is common risk factors. 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.

How Asthma May Cause Lung Cancer

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.

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.

Reducing Lung Cancer Risk with Asthma

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.

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 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