Is smoking an independent risk factor for developing cervical intra-epithelial neoplasia and cervical cancer? A systematic review and meta-analysis.

Introduction: Cervical cancer is the fourth most common form of cancer among women. Smoking tobacco seems to be a risk factor for the development of cervical intra-epithelial neoplasia (CIN) and cervical cancer, but the exact role of smoking in the process of cervical carcinogenesis is not known. The aim of this study is to investigate the relationship between smoking and the development of CIN and cervical cancer. Areas covered: We searched Embase, Medline, Cochrane Central, Web of Science, and Google Scholar for studies on smoking and CIN and cervical cancer, published between 2009 and 2018. The following were the outcomes: CIN3 alone, CIN2 and CIN3 combined, CIN2+, CIN3+, and cervical cancer alone. We included 49 studies in our review and 45 in our meta-analyses. Expert opinion: Based on the available evidence it can be - cautiously - concluded that smoking increases the risk of cervical abnormalities. However, the high risk of bias indicates that for future studies, it will be important to adjust for relevant predictors, to separate CIN from cervical cancer as outcome measures, and to report research methods in detail.