Parity and endometrial cancer risk: a meta-analysis of epidemiological studies

Qi-Jun Wu, Yuan-Yuan Li, Chao Tu, Jingjing Zhu, Ke-Qing Qian, Tong-Bao Feng, Changwei Li, Lang Wu, Xiao-Xin Ma
2015 Scientific Reports  
The association between parity and endometrial cancer risk is inconsistent from observational studies. We aimed to quantitatively assess the relationship by summarizing all relevant epidemiological studies. PubMed (MEDLINE), Embase and Scopus were searched up to February 2015 for eligible case-control studies and prospective studies. Random-effects model was used to pool risk estimations. Ten prospective studies, 35 case-control studies and 1 pooled analysis of 10 cohort and 14 case-control
more » ... ies including 69681 patients were identified. Pooled analysis revealed that there was a significant inverse association between parity and risk of endometrial cancer (relative risk (RR) for parous versus nulliparous: 0.69, 95% confidence interval (CI) 0.65-0.74; I 2 = 76.9%). By evaluating the number of parity, we identified that parity number of 1, 2 or 3 versus nulliparous demonstrated significant negative association (RR = 0.73, 95% CI 0.64-0.84, I 2 = 88.3%; RR = 0.62, 95% CI 0.53-0.74, I 2 = 92.1%; and RR = 0.68, 95% CI 0.65-0.70, I 2 = 20.0% respectively). The dose-response analysis suggested a nonlinear relationship between the number of parity and endometrial cancer risk. The RR decreased when the number of parity increased. This meta-analysis suggests that parity may be associated with a decreased risk of endometrial cancer. Further studies are warranted to replicate our findings. As the most common tumor of the female reproductive tract, endometrial cancer remains the fourth most common malignancy in females 1 . Parity, a representative reproductive factor, is demonstrated to potentially modulate risk of endometrial cancer through affecting estrogen and progesterone levels 2 . A lot of observational studies also suggest such an association. For example, in comparison to nulliparous, parous was detected to be associated with decreased risk of developing endometrial cancer in several prospective studies 3,4 , case-control studies 5-12 , as well as pooled analysis 13 . However, such an inverse association was not detected in several other epidemiological studies [14] [15] [16] [17] . Considering that results from individual epidemiological studies can be strongly affected by available sample sizes, a better way to clarify the association between parity and risk of endometrial cancer is to summarize all available evidence from relevant observational studies. In the current study, we aimed to conduct a comprehensive meta-analysis to evaluate this research question. We also conducted analysis to clarify the dose-response relationship between number of parity and risk of endometrial cancer. Results Literature Search and Study Characteristics. The detailed procedures of the literature search and article screening were demonstrated in Fig. 1 . The database search yielded 7906 publications, among which 7852 were excluded based on the screening of titles and/or abstracts. Combined with 35 studies identified through manual search of references of relevant review articles, the whole contents of a total of 89 publications were assessed. Among them, 43 articles were further excluded due to various reasons: 5 did not meet the eligibility criteria; 20 involved duplicated study individuals with other articles; and 18 did not report sufficient data or information (the complete list of the 43 excluded articles is available upon request). Finally, a total of 46 studies were included in the current meta-analysis (references are within the supplementary material). The detailed characteristics of the involved studies were demonstrated in Table 1 . In total, 10 prospective cohort studies, 35 case-control studies and 1 pooled analysis of 10 cohort and 14 case-control studies were involved. Overall, 18 studies were conducted in Europe, 18 in America, 9 in Asia, and 1 was an international report. The studies enrolled 69681 patients. The quality assessments of these studies were demonstrated in Tables 2 and 3 . Overall, 9 of the 10 cohort studies (90%) and 26 of the 35 case-control studies (74%) were categorized as high-quality studies. Others were categorized as low-quality studies.
doi:10.1038/srep14243 pmid:26373341 pmcid:PMC4642705 fatcat:7vxngl47zfgqblot5zpk5iayy4