Does smoking increase risk of ovarian cancer? A systematic review

Objectives. Although early reports suggested that smoking was not associated with ovarian cancer risk, recent studies have reported positive associations for cancers of the mucinous subtype. We sought to clarify the relationship between smoking and ovarian cancer by histological subtype. Methods. We conducted a systematic literature review and meta-analysis of studies investigating the association between smoking and risk of the different histological subtypes of epithelial ovarian cancer. Eight population-based case-control studies, one pooled analysis of case-control studies, and one cohort study met the inclusion criteria. Summary relative risks (RR), 95% confidence intervals (CI), and tests for heterogeneity were generated from random effects models. Results. Combined, these studies included a total of 910 women with mucinous and 5564 with non-mucinous ovarian cancers. There was a significant doubling of risk of mucinous ovarian cancer in current smokers compared to never smokers (summary RR 2.1, 95%CI 1.7-2.7), but no increased risk of serous (1.0, 95%CI 0.8-1.2) or endometrioid (0.8, 95%CI 0.6-1.1) cancers and a significant risk reduction for clear cell cancers (0.6, 95%CI 0.3-0.9). The risk of mucinous cancer increased with increasing amount smoked but returned to that of never smokers within 20-30 years of stopping smoking. Conclusions. Meta-analysis suggests that current smoking doubles a woman's risk of developing mucinous ovarian cancer. Stopping smoking returns the risk to normal in the long term. Smoking may thus be one of the few modifiable factors offering potential for primary prevention of mucinous ovarian cancer. (c) 2006 Elsevier Inc. All rights reserved.