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

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, P = 0.049); 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, P = 0.021). 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, P = 0.004). 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.

Breastfeeding and thyroid cancer risk in women: A dose-response meta-analysis of epidemiological studies

“…Our analyses summarized evidence from epidemiological studies and demonstrated that breastfeeding could potentially decrease thyroid cancer risk in women. Our study provides new knowledge beyond other meta-analyses and systematic reviews [35, 36]. …”

“…Since the conduction of the current study, several meta-analyses focusing on similar research questions have been published [35, 36]. In the study by Cao et al [35], duration of breastfeeding was significantly associated with decreased thyroid cancer risk in cohort studies. The association of breastfeeding duration in overall studies and the associations of breastfeeding were not statistically significant.…”

Female Reproductive Factors and Differentiated Thyroid Cancer

“…More recently, two meta-analyses showed postmenopausal status and older age at menopause to be, respectively, associated with a borderline significant reduction (RR 0.79, 95% CI 0.62–1.01) (32) and increase (RR 1.24, 95% CI 1.00–1.53) (33) of DTC risk. A further meta-analysis focusing on PTC only, also found late age at menopause to be associated with increased PTC risk (RR = 1.39, 95% CI 1.03–1.89) (34).…”

Are pregnancy, parity, menstruation and breastfeeding risk factors for thyroid cancer? Results from the Korea National Health and Nutrition Examination Survey, 2010‐2015

“…Second, breastfeeding appeared to decrease the risk of thyroid cancer. Several previous studies have shown that breastfeeding could lower thyroid cancer risk . In addition, Mack et al have demonstrated that the use of lactation suppressants could increase the risk of thyroid cancer .…”