Parity and thyroid cancer risk: a meta‐analysis of epidemiological studies

Abstract

Although observational studies have assessed the relationship between parity and thyroid cancer risk, the findings are inconsistent. To quantitatively assess the association, we conducted a systematic review and meta‐analysis. PubMed and Embase were searched up to January 2015. Prospective or case–control studies that evaluated the association between parity and thyroid cancer risk were included. We used the fixed‐effects model to pool risk estimates. After literature search, 10 prospective studies, 12 case‐control studies and 1 pooled analysis of 14 case‐control studies including 8860 patients were identified. The studies had fair methodological quality. Pooled analysis suggested that there was a significant association between parity and risk of thyroid cancer (RR for parous versus nulliparous: 1.09, 95% CI 1.03‐1.15; I2=33.4%). The positive association persisted in almost all strata of subgroup analyses based on study design, location, study quality, type of controls, and confounder adjustment, although in some strata statistical significance was not detected. By evaluating the number of parity, we identified that both parity number of 2 versus nulliparous and parity number of 3 versus nulliparous demonstrated significant positive associations (RR=1.11, 95% CI 1.01‐1.22; I2=31.1% and RR=1.16, 95% CI 1.01‐1.33; I2=19.6% respectively). The dose‐response analysis suggested neither a non‐linear nor linear relationship between the number of parity and thyroid cancer risk. In conclusion, this meta‐analysis suggests a potential association between parity and risk of thyroid cancer in females. However, the lack of detection of a dose‐response relationship suggests that further studies are needed to better understand the relationship.

Gender in Endocrine Diseases: Role of Sex Gonadal Hormones

“…It can be hypothesized that female sex hormones (i.e., estrogens and progesterone) and their particular patterns may be involved in explaining the higher prevalence of thyroid diseases in females [ 37 – 39 ]. Differentiated thyroid carcinoma (DTC), the most common endocrine neoplasm, is also more common in women than in men, but evidence regarding gender-related differences is scant [ 40 ]. According to recent data, the age-adjusted incidence ratio of thyroid cancer in 2013 was 21.61/100,000 women and 7.26/100,000 men, for a female-to-male ratio of almost 3 : 1.…”

Other Primary Malignancies Among Women With Adult-Type Ovarian Granulosa Cell Tumors

“…11 It has been proposed that female hormones, reproductive factors, and obesity also play a role in thyroid cancer pathogenesis, but there are no consistent data that link ovarian and thyroid cancer. 28,29 DICER1 germline mutation carriers have a predisposition to both thyroid cancer and sex cord-stromal, particularly Sertoli-Leydig cell tumors. 30,31 Cancer registry data are not, however, molecularly validated, and there is a possibility that some tumors identified as AGCT may actually represent other sex cord-stromal tumors.…”

Thyroid cancer incidence and mortality in Latin America

“…Other possible risk factors associated with women are sex hormones in interaction with the Thyroid-Stimulating Hormone (TSH), which can play a critical role in the development of thyroid malignancy, as well as advanced age in menopause and the greater parity (28, 29). In men, it was found a positive association with the story of goiter, thyroid nodules and family history of cancer (30).…”