The contextual details of subgroup analysis included in this meta-analysis.

HWE: Hardy-Weinberg Equilibrium; WBC: White blood cells; BALF: bronchoalveolar lavage fluid; NA: not available.
*: The HWE test results of CYP1A1 Msp1 that could be calculated were shown in the table, and the items with * meant the result that had been reported in the articles.
: Due to different setting of smoking status in papers, people who had smoked were calculated as smokers.
ORa: Adjusted OR. ED: Epidemiological Design; NED: Non-epidemiology Design; WBC: blood, White blood cell lymphocytes, and serum. ζ: Newcastle-Ottawa Scale (NOS).
: The OR 95% CI was captured from logistic analysis; I: Heavy-smoker; a: healthy control; b: hospital control.
: The GSTM1 data of this study was omitted because of a bigger sample in the other study published in the same year.