COPD, short for chronic obstructive pulmonary disease, is linked to a heightened risk of lung cancer in people who have never smoked, indicates research published online in the journal Thorax.
The risk is on a par with that of smokers without chronic lung disease, the findings indicate.
COPD is an umbrella term for respiratory conditions that narrow the airways, such as bronchitis and emphysema. Smoking is the main risk factor for COPD, which itself is associated with a heightened risk of developing lung cancer.
But up to 39% of people who develop COPD have never smoked, and it's not clear what their risk of lung cancer is, because most of the studies looking at this have included too few participants.
To explore this further, the researchers drew on data from the National Health Insurance Service (NHIS) National Sample Cohort study, involving a representative sample of Korean citizens.
For the purposes of the current study, the researchers included 338,548 men (146,996) and women (191,552) between the ages of 40 and 84, with no history of lung cancer, who had had at least one health check provided by NHIS between 2002 and 2013.
Their health was tracked for an average of 7 years, based on inpatient and outpatient treatment and prescriptions issued.
During this monitoring period, 1834 participants developed lung cancer. In 290 cases, the person had COPD, but in 1544 cases, the person didn't.
Among current and former smokers, those without COPD were around twice as likely to develop lung cancer while 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, people with COPD were more than 2.5 times as likely to develop lung cancer as those without COPD, the data analysis showed.
What's more, the risk of lung cancer in those with COPD, but who had never smoked, was on a par with that of smokers without COPD, the findings indicate.
"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," write the researchers.
They acknowledge that the severity of COPD wasn't assessed, nor were they able to glean information on environmental and occupational exposures, all of which may have influenced the development of lung cancer.
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.
Peer reviewed? Yes
Evidence type: Observational cohort study