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BioMed Research International
Volume 2015, Article ID 103515, 10 pages
http://dx.doi.org/10.1155/2015/103515
Review Article

Reproductive Factors but Not Hormonal Factors Associated with Thyroid Cancer Risk: A Systematic Review and Meta-Analysis

1Reproductive Center, Central Hospital of Xuzhou, Affiliated Xuzhou Hospital of Southeast University, Xuzhou 221009, China
2Department of Anesthesia, People’s Hospital of Zhucheng, Zhucheng 262200, China
3Reproductive Center, The Affiliated Hospital of Weifang Medical University, Weifang 261000, China
4Department of General Surgery, Central Hospital of Xuzhou, Affiliated Xuzhou Hospital of Southeast University, Xuzhou 221009, China

Received 4 October 2014; Accepted 16 March 2015

Academic Editor: Ondrej Topolcan

Copyright © 2015 Yijuan Cao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Many studies have investigated the association between hormonal and reproductive factors and thyroid cancer risk but provided contradictory and inconclusive findings. This review was aimed at precisely estimating this association by pooling all available epidemiological studies. 25 independent studies were retrieved after a comprehensive literature search in databases of PubMed and Embase. Overall, common hormonal factors including oral contraceptive and hormone replacement therapy did not alter the risk of thyroid cancer. Older age at menopause was associated with weakly increased risk of thyroid cancer in overall analysis (RR = 1.24, 95% CI 1.00–1.53, ); however, longer duration of breast feeding was related to moderately reduced risk of thyroid cancer, suggested by pooled analysis in all cohort studies (RR = 0.7, 95% CI 0.51–0.95, ). The pooled RR in hospital-based case-control studies implicated that parous women were more susceptible to thyroid cancer than nulliparous women (RR = 2.30, 95% CI 1.31–4.04, ). The present meta-analysis suggests that older age at menopause and parity are risk factors for thyroid cancer, while longer duration of breast feeding plays a protective role against this cancer. Nevertheless, more relevant epidemiological studies are warranted to investigate roles of hormonal and reproductive factors in thyroid carcinogenesis.