Nineteen studies were included for review (471,542 participants). These included one clinical trial (39,876 participants), seven cohort studies (348,079 participants), six case-control studies (15,343 participants) and five nested case-control studies (68,244 participants).
There was no significant association between aspirin use and lung cancer risk in cohort and clinical trials (RR 0.96, 95% CI 0.78 to 1.19; eight studies; 387,936 participants) or with case-control studies (OR 0.87, 95% CI 0.69 to 1.09; nine studies; 31,266 participants). Excluding the clinical trial did not significantly alter the results. There was evidence of substantial heterogeneity for cohort studies (Ι²=88%) and case-control studies (Ι²=92%).
There was no significant association between non-aspirin NSAID (non-steroidal anti-inflammatory drug) use and lung cancer risk with cohort studies (RR 0.93, 95% CI 0.77 to 1.12; two studies; 104,287 participants) or case-control studies (OR 0.88, 95% CI 0.67 to 1.16; five studies; 26,310 participants). There was evidence of moderate heterogeneity for cohort studies (Ι²=52%) and substantial heterogeneity for case-control studies (Ι²=93%).
Overall NSAID use was not associated with lung cancer risk in case-control studies (OR 0.80, 95% CI 0.63 to 1.03; six studies; 52,913 participants). There was evidence of substantial heterogeneity (Ι²=94%).
Consuming seven or more NSAID tablets a week was associated with a significantly reduced risk of lung cancer (OR 0.80 95% CI 0.67 to 0.95; three studies; 15, 507 participants). There was no evidence of heterogeneity (Ι²=0%).
Gender, histology and duration of use were not associated with lung cancer risk.
Risk ratios or odds ratios with 95% confidence intervals were reported for individual studies according to smoking status.
Sensitivity analyses did not significantly alter the results of the meta-analyses.
Examination of funnel plots found no evidence of publication bias.