Contracting illnesses like COVID-19, severe flu, or pneumonia significantly increases the risk of developing lung cancer, suggests recent research findings. According to a study published in the journal Cell, these viral infections can essentially ‘reprogram’ the lungs, making them more susceptible to cancerous growths, potentially months or even years after the initial illness.

Jie Sun, PhD, a researcher at the University of Virginia School of Medicine, explains that this occurs because the lungs remain in an inflamed state following the infection. “A severe case of COVID or flu can leave the lungs in a long-lasting inflamed state, making it easier for cancer to establish itself later,” Sun noted.

Respiratory infections, including the flu and COVID-19, are prevalent causes of lung injury and trauma. However, the long-term implications of these infections on cancer risk have remained largely unclear until now.

To delve deeper into this issue, Sun and his team conducted studies on both laboratory mice and human patients, examining how these infections affect the lungs over time. The research provides critical insights into how viral infections can influence long-term health outcomes, particularly concerning cancer risk.

Respiratory infections – such as flu and covid – are one of the most common causes of injury and trauma to the lungs, but scientists have had little understanding of the effects this can have on a patient’s long-term cancer risk. 

To investigate, Sun and his team looked at the effects in both lab mice and human patients. 

In mice, they found that the animals that suffered severe lung infections were both more likely to go on to develop lung cancer and significantly more likely to die from the disease. 

And when they looked at data from human subjects, they saw a similar pattern, noting a significant association between people who had been hospitalised for covid and increased lung cancer incidence. 

They noted a significant link between people who had been hospitalised for covid and increased lung cancer incidence 

Furthermore, the 1.24-fold increase was true regardless of ‘comorbidities’ such as smoking, or having other health conditions. 

Using learnings from the mice model, the researchers concluded that viral lung infections have dramatic effects on immune cells called neutrophils and macrophages.

These are supposed to protect the lungs, but the viruses triggered some of the neutrophils to malfunction and create an inflamed, ‘pro-tumor’ environment where cancer can thrive, months or even years later. 

Similarly, the scientists also identified significant changes to the epithelial cells that line the lungs and the air sacs that let us breathe.

The findings will terrify the millions of survivors of severe covid-19 who may now face increased chances of developing lung cancer in the years ahead – but there was good news for people who had been vaccinated. 

Prior vaccination appeared to prevent the cancer-promoting lung changes, and in people who had only experienced a mild case of covid, actually slightly reduced their cancer risk. 

Sun said: ‘The encouraging news is that vaccination largely prevents those harmful changes for cancer growth in the lung.

‘We also believe that vaccines don’t just prevent acute hospitalisation after contracting the virus.

 ‘They may also reduce the long-term fallout of severe infection, including the kind of immune scarring that can increase cancer risk.’

Based on their findings, the scientists are urging doctors to closely monitor patients who have recovered from severe covid, flu or pneumonia in hopes of catching lung cancer early, when it is most treatable.

Jeffrey Sturek, MD, PhD, a UVA physician-scientist and collaborator on the study said that he hopes that this will change the notion of who is at risk of lung cancer. 

He said:  ‘These findings have important immediate implications for how we monitor patients after severe respiratory viral infection.

‘We’ve known for a long time that things like smoking increase the risk for lung cancer. The results from this study suggest that we may need to think about severe respiratory viral infection similarly. 

‘For example, in some patients who are at high risk for lung cancer based on smoking history, we recommend close monitoring with routine screening CT scans of the lungs to catch cancer early. In future studies, we may want to consider a similar approach after severe respiratory viral infection.’

Lung cancer is the UK’s biggest cancer killer, according to the Lung Cancer Coalition, claiming more than 35,000 lives every year.

Around a quarter of those diagnosed with the disease every year are non-smokers.