Facts and fiction of the relationship between preexisting tuberculosis and lung cancer risk: a systematic review.

There has been conflicting evidence concerning the possible association between tuberculosis (TB) and subsequent risk of lung cancer. To investigate whether currently published epidemiological studies can clarify this association, we performed a systematic review of 37 case-control and 4 cohort studies (published between January 1966 and January 2009) and a meta-analysis of risk estimates, with particular attention to the role of smoking, passive smoking and the timing of diagnosis of TB on this relationship. Data for the review show a significantly increased lung cancer risk associated with preexisting TB. Importantly, the association was not due to confounding by the effects of tobacco use (RR=1.8, 95% confidence interval (CI)=1.4-2.2, among never smoking individuals), lifetime environmental tobacco smoke exposure (RR=2.9, 95%CI=1.6-5.3, after controlling) or the timing of diagnosis of TB (the increased lung cancer risk remained 2-fold elevated for more than 20 years after TB diagnosis). Interestingly, the association was significant with adenocarcinoma (RR=1.6, 95%CI=1.2-2.1), but no significant associations with squamous and small cell type of lung cancer were observed. Although no causal mechanism has been demonstrated for such an association, present study supports a direct relation between TB and lung cancer, especially adenocarcinomas.