Patients previously diagnosed with some kinds of chronic respiratory disease face an increased risk of lung cancer, analysis of a large number of scientific studies suggests.
Three common diseases of the respiratory system, including bronchitis, pneumonia and emphysema were linked to an elevated risk of subsequent lung cancer, the researchers said.
Two others -- asthma and tuberculosis -- were not found to increase cancer risk, they said.
The conclusion was the result of a breakdown of seven studies that surveyed 25,000 people with some form of respiratory illness.
The researchers compared patients who were diagnosed with a respiratory disease against a control group of patients who were not.
"Associations between various respiratory diseases and lung cancer have been shown in earlier studies, but few of these studies considered multiple respiratory diseases simultaneously," said study author Dr. Ann Olsson at the International Agency for Research in Cancer in France.
The analysis was conducted on behalf of the American Thoracic Society, and was adjusted for age, work in occupations involving elevated risks of lung cancer, education level and smoking habits.
People diagnosed with all three respiratory diseases -- chronic bronchitis, pneumonia and emphysema -- faced a greater risk of developing lung cancer than those diagnosed with only chronic bronchitis, the researcher found.
The fact that respiratory illnesses can have different impacts on lung cancer risks could be down to different underlying mechanisms involved in each disease, Olsson said.
"Better understanding of these associations may help guide the type and frequency of clinical surveillance needed for patients with each of these diseases," she said.
Chronic Obstructive Pulmonary Disease, the official medical term for such respiratory diseases, is the third leading cause of death in the United States, the American Lung Association says.
In 2011, as many as 12.7 million U.S. adults were suffering from some form of COPD, it said.
The number one risk factor for development of COPD is smoking, followed by air pollution, then second-hand smoke followed by dust and chemical association with certain occupations, the association said.
Other studies have linked sodium intake, obesity and high blood pressure to the list of risks.
There is also often a family history of respiratory infections and disease, the ALA said.
The researchers took pains to point out that while the finding showed an association of lung cancer risk with certain respiratory diseases, it does not demonstrate a direct cause-and-effect relationship.