Ortega-Olvera C, et al. - Researchers performed a population-based case-control study to evaluate the relationship between serum thyroid hormone concentration (thyroxine and triiodothyronine) and breast cancer (BC) and how obesity can influence this relationship as an effect modifier in premenopausal and postmenopausal women. A strong relationship between BC and serum concentrations of total triiodothyronine (TT3) and total thyroxine (TT4) was found. In both premenopausal and postmenopausal women, lower TT3 concentrations were related to BC and no effect modification was noted.

Methods

• For this investigation, serum thyroid hormone and thyroid antibody levels were measured in 682 subjects with incident breast cancer (cases) and 731 controls who took part in a population-based case-control study performed from 2004 to 2007 in three states of Mexico.
• Researchers tested the relationship of TT4 and TT3 stratifying by menopausal status and body mass index (BMI), and adjusted for other health and demographic risk factors utilizing logistic regressions models.

Results

• In both premenopausal (odds ratio (OR) _{per standard deviation} = 5.98, 95% CI 3.01–11.90) and postmenopausal women (OR _{per standard deviation} = 2.81, 95% CI 2.17–3.65), higher serum TT4 concentrations were related to BC.
• In premenopausal women, the impact of TT4 diminished as BMI increased, while the inverse was seen in postmenopausal women.
• It was observed that the significance of the effect modification was marginal (p=0.059) in postmenopausal women and was not significant in premenopausal women (p=0.22).
• They found that lower TT3 concentrations were correlated with BC in both premenopausal and postmenopausal women and no effect modification was noted.