Cigarette smoking and risk of uterine myoma: Systematic review and meta-analysis

Objective To review the literature on the relationship between smoking and the risk of uterine myoma, we conducted a systematic review and a meta-analysis of published studies. In this meta-analysis, we included all identified studies of association between smoking and uterine myoma where these were case-control or cohort studies, reporting original data, ultrasound or histological confirmed diagnosis of myomas and information on the association between tobacco smoking and myomas. Study design We carried out a literature search on MEDLINE/EMBASE of all studies published as original articles in English up to October 2015, using the Medical Subject Heading terms and free search terms about myoma and smoking. We selected only studies published in English. Moreover, bibliographies of the retrieved papers were reviewed, to identify any other relevant publication. A total of 14 different studies were eligible for a qualitative synthesis and data extract from 10 studies were combined in a meta-analysis. Results The summary OR of former compared to never smokers was 0.93 (0.88-0.99) with no heterogeneity. The summary OR of current smokers compared to never smokers, was 0.83 (0.65-1.04), even if the subtotal OR in cohort studies was 0.85 (0.73-0.98) with no heterogeneity. When sensitivity analysis was performed the summary OR was 0.83 (0.71-0.97). Conclusion The primary meta-analyses found no significant effect of smoking on risk of uterine myoma. Subgroup analysis for study design showed a small risk reduction for current and former smokers in cohort studies. A sensitivity analysis showed an inverse association between ever smoking and uterine myoma. However, given the limited number of studies in each sub-analysis, weak associations and the absence of a dose dependent effect, caution should be paid in the interpretation of these findings and further investigation are needed.