Smoking Is the Most Significant Modifiable Lung Cancer Risk Factor in Systemic Lupus Erythematosus

To assess lung cancer risk in systemic lupus erythematosus (SLE), relative to demographics, drug exposures, smoking, and disease activity.

We analyzed data from 14 SLE cohorts. We calculated adjusted HR estimates for lung cancer in SLE, relative to demographics, smoking, time-dependent medication exposures, and cumulative disease activity [mean adjusted SLE Disease Activity Index (SLEDAI) scores]. This project was approved by the ethics boards of all participating institutions, including the Institutional Review Board of the McGill University Health Centre. The ethics approval number for the Cancer Risk study is GEN-06-031.

Within these 14 SLE cohorts, 49 incident lung cancers occurred. Among lung cancer cases, 59.0% were in the highest SLEDAI quartile at baseline versus 40.8% of lung cancer-free SLE controls. The vast majority (84.2%) of SLE lung cancer cases were ever-smokers at baseline, versus 40.1% of those without lung cancer. In adjusted models, the principal factors associated with lung cancer were ever smoking (at cohort entry) and current age. Estimated adjusted effects of all drugs were relatively imprecise, but did not point toward any drug exposures as strong lung cancer risk factors.

We saw no clear evidence for drugs as a trigger for lung cancer risk in SLE, although drug risk estimates were relatively imprecise. Smoking may be the most significant modifiable lung cancer risk factor in SLE.