Contrary to what some observers believe, a new study concludes that chronic obstructive pulmonary disease (COPD) is not an independent risk factor for lung cancer.

The findings were published in the January 2013 issue of the International Association for the Study of Lung Cancer’s (IASLC) Journal of Thoracic Oncology. The University of Nottingham researchers studied patients with lung cancer between January 2000 and July 2009 from The Health Improvement Network, a general practice database, in the United Kingdom.

COPD and lung cancer are two of the most prevalent smoking-related diseases worldwide. The researchers “found evidence of a strong association between COPD and lung cancer, but this was largely explained by the effect of smoking and is most apparent in recently diagnosed cases of COPD, suggesting a strong element of ascertainment bias.”

The study also pointed to “an extremely strong unadjusted relationship between both COPD and pneumonia and lung cancer in the six months immediately before lung cancer diagnosis. This is useful in a clinical context, highlighting the need to consider a diagnosis of lung cancer when making new diagnoses of COPD or pneumonia.”

The researchers support the American Thoracic Society and the U.K. National Institute for Health Research recommendation that patients should have a chest x-ray to detect lung cancer at the time of the COPD diagnosis.