Patients With COPD and No Smoking History Face Greater Risk of Lung Cancer, Study Says

Chronic obstructive pulmonary disease (COPD) is already associated with an increased risk of developing lung cancer, and smoking is the major risk factor for both diseases. Now, a new study says that patients with COPD—even if they never smoked—have a 2.6 times greater incidence of developing lung cancer compared with those who had neither COPD or a history of smoking.

Research appearing Thursday in Thorax said that the risk was comparable to that of smokers who did not have COPD.

Lung cancer screening is already complicated and underutilized, according to previous studies. With these new results, should patients with COPD be considered possible candidates for lung cancer screening, irrespective of smoking status? Future research is needed to answer that question, the authors said.

Up to 39% of people who develop COPD have never smoked. It has not been well understood what their risk of lung cancer is, because most of previous studies on this topic have included too few participants.

However, this large-scale study used data from the National Health Insurance Service (NHIS) National Sample Cohort study, which includes a representative sample of Korean citizens.

The researchers included 338,548 individuals between the ages of 40 and 84 years, with no history of lung cancer, who had had at least 1 health check provided by NHIS between 2002 and 2013. The group was split by 146,996 men and 191,552 women.

Their health was tracked for an average of 7 years (or 2.4 million person-years of follow-up), based on inpatient and outpatient treatment and prescriptions issued.

Patients with COPD were older and more likely to be male, smokers, and to have a lower income and more comorbidities, according to the Charlson Comorbidity Index.

During the follow-up period, there were 290 incident cases of lung cancer in participants with COPD (incidence rate 4.9 per 1000 person-years).

In those without COPD (or before developing COPD) there were 1544 cases (incidence rate 0.7 per 1000 person-years), for a total of 1834 individuals developing lung cancer. Of those, COPD was present in 290 cases. But in 1544 cases, there was no COPD.

Among current and former smokers, those without COPD were around twice as likely to develop lung cancer, and those with COPD were 6 times as likely to do so, compared with people who had never smoked and didn’t have COPD.

But after taking account of potentially influential factors, among those who had never smoked, individuals with COPD were more than 2.5 times as likely to develop lung cancer as those without COPD, the data analysis showed.

“Given that poor lung function in COPD is often a barrier to optimal lung cancer treatment due to increased risk of treatment related morbidities, our study suggests that early detection of lung cancer in COPD patients may reduce the risk of treatment complications,” the researchers said in a statement.

The study had several limitations:

• Researchers could not evaluate the impact of COPD severity on lung cancer incidence because spirometry findings were not available.
• There was no information on environmental or occupational exposures, or the severity of emphysema, both of which are potential confounders for increased lung cancer risk in COPD.
• Lastly, because the data on clinical outcomes were based on claims data, there might be misclassification of COPD or lung cancer. But the researchers said that data is considered to be reliable.

Nevertheless, they suggest their findings indicate that COPD is a strong independent risk factor for lung cancer.

“Future studies should evaluate whether COPD patients are candidates for lung cancer screening, irrespective of smoking status,” they conclude.

Reference

Park HY, Kang D, Shin SH, et al. Chronic obstructive pulmonary disease and lung cancer incidence in never smokers: a cohort study [published online April 2, 2020]. Thorax. doi: 10.1136/thoraxjnl-2019-213732.