Hormonal and reproductive risk factors of papillary thyroid cancer: A population-based case-control study in France

- The incidence of thyroid cancer is higher in women compared to men.
- The risk increases with a shorter time interval between menarche and menopause.
- The risk increases after menopause or ovariectomy.
- The risk decreases with use of oral contraceptives and menopausal hormone therapy.
- Breast-feeding reduces the risk.

The three times higher incidence of thyroid cancer in women compared to men points to a role of female sex hormones in its etiology. However the effects of these factors are poorly understood. We analyzed the association between thyroid cancer and hormonal and reproductive factors among women enrolled in CATHY, a population-based case-control study conducted in France. The study included 430 cases of papillary thyroid cancer and 505 controls frequency-matched on age and area of residence. The odds ratios for thyroid cancer increased with age at menarche (p trend 0.05). Postmenopausal women were at increased risk, as compared to premenopausal women, particularly if menopause followed an ovariectomy, and for women with age at menopause < 55 years. In addition, use of oral contraceptives and menopausal hormone therapy reduced the association with thyroid cancer by about one third, and breastfeeding by 27%. Overall, these findings provide evidence that the risk of thyroid cancer increases with later age at menarche and after menopause, and decreases with use of oral contraceptives and menopausal hormone therapy. These findings confirm an implication of hormonal factors in papillary thyroid cancer risk, whose mechanisms need to be elucidated.