Purpose: Several studies have assessed the association between asthma and cancer but none of them revealed a clear pattern of association. We aimed to examine the association between asthma, chronic obstructive pulmonary disease (COPD), and cancer.
Methods: We performed a cohort study with a nested case-control analysis using the General Practitioner Research Database in the UK. We defined three cohorts: patients with asthma, patients with COPD, and general population. During the follow-up, we identified a total of 5263 incident cases of cancer. We conducted a nested case-control analysis that included all cancer cases as well as 20 000 controls free of cancer frequency-matched on age, sex, and calendar year.
Results: Patients with asthma did not have an overall greater risk of cancer compared with the general population (odds ratio = 0.93, 95% confidence interval (CI): 0.86-1.00). However, they presented an elevated risk of experiencing lung cancer (odds ratio = 1.84, 95%CI: 1.58-2.15). Controlling for smoking and other potential confounding factors yielded a lower estimate (odds ratio = 1.35, 95%CI: 1.15-1.59). This estimate contrasted with that observed for non-smoking related cancer (0.87, 95%CI: 0.80-0.94). Overall, respiratory drugs did not seem to be associated with cancer among asthmatic patients. Patients with COPD had an Odds ratio of cancer of 1.26 (95%CI: 1.12-1.43) compared with the general population.
Conclusions: Asthma was not associated with an increased risk of cancer. In fact, the risk of non-smoking related cancer was slightly reduced. However, we observed a small-elevated risk of lung cancer among asthmatic patients. Whether this result is a due to residual confounding and/or protopathic bias remains unclear. Further investigation is warranted to confirm or discard these associations.
Copyright 2005 John Wiley & Sons, Ltd.