Endocrine Abstracts

JOINT741

Purpose: Aromatase inhibitors are frequently used in adjuvant therapy for both early- and advanced-stage breast cancer. While the common side effects of these treatments are well-documented, their impact on thyroid function has not been systematically assessed and remains unclear. This study aimed to evaluate thyroid function in postmenopausal women with estrogen receptor-positive early-stage breast cancer one and two years after starting aromatase inhibitors.

Methods: This prospective controlled study involved 59 postmenopausal women with early-stage breast cancer and 39 healthy controls. All participants underwent chemotherapy and were treated with aromatase inhibitors, with 35 patients also receiving locoregional radiotherapy. The primary outcomes included the evaluation of thyroid hormones and thyroid-binding globulin post-chemotherapy, as well as at one-year and two-year follow-ups after initiating aromatase inhibitors. Secondary outcomes included thyroid autoantibodies and body mass index.

Results: No significant differences in thyroid parameters were observed between patients and healthy controls before chemotherapy. During treatment with aromatase inhibitors, free thyroxine levels increased at both follow-up visits (P <0.01) and total thyroxine levels increased at the two-year visit (P = 0.02). In contrast, triiodothyronine levels decreased at both visits (P <0.01 and P = 0.03). There were no changes in thyroid-stimulating hormone or thyroid-binding globulin, but albumin levels increased after one year (P <0.01). Weight changes were insignificant, and the prevalence of autoimmune thyroiditis was low (≤15%). No differences in thyroid function were detected between women treated with locoregional radiotherapy and those who were not.

Conclusions: This study suggests that, despite statistically significant changes in peripheral thyroid hormones, no obvious clinically important effects were observed in patients with early-stage breast cancer during the two years of treatment with aromatase inhibitors. These changes were not associated with thyroid autoimmunity, non-thyroidal illness, radiotherapy, or high-dose corticosteroids. To our knowledge, this study provides the longest follow-up of thyroid hormones and thyroid-binding globulin in this specific patient group, focusing on the effects of aromatase inhibitors on thyroid function. Further research is needed to understand better the long-term impact of aromatase inhibitors on thyroid function in this population.