Night work and cancer: A systematic review and meta-analysis.

1604 Background: The association between night work (or shift work) and cancers has been studied for decades. However, researches investigating the association have yielded inconsistent results. Methods: A systematic review and meta-analysis was performed to investigate whether night work is a risk factor for different kinds of cancer. PubMed and Cochrane library search were independently conducted by two authors from January 1960 to January 2013 using keywords related to night work and cancer. According to between-studies heterogeneity, pooled risk ratios (RR) were estimated with fixed or random effects models by STATA 12.0 software. Sensitivity analysis and publication bias were also analyzed. Results: A total of 33 studies were identified according to the inclusion criteria. The aggregate estimate for all cancers combined was [1.35, (1.24-1.47)] with a similar significant elevation of breast cancer [1.36, (1.21-1.52)], ovary cancer [1.24, (1.08-1.43)] risk among female, and malignant melanoma [1.58, (1.03-2.44)]. No significant risks were observed as regard to patients with prostate cancer, colorectal cancer, cervix cancer and non-Hodgkin lymphoma. Sensitivity analyses indicated no change in all results but malignant melanoma and colorectal cancer. The RRs became significant differences after removing one study from the colorectal cancer [1.60, (1.70-2.18)]. No publication bias was observed in this meta-analysis. Conclusions: The current meta-analysis suggested that night work played an important role in breast cancer, ovary cancer, and malignant melanoma. However, it might be premature to consider night work as a risk factor for prostate cancer, colorectal cancer, cervix cancer and non-Hodgkin lymphoma. [Table: see text]