Impact of aromatase inhibitors on thyroid function in postmenopausal women with early-stage breast cancer: a prospective controlled study

PURPOSE: Aromatase inhibitors are commonly used in adjuvant therapy for breast cancer. However, their impact on thyroid function remains unclear. This study aimed to evaluate thyroid function in postmenopausal women with oestrogen-receptor-positive early-stage breast cancer one and two years after initiating 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 aromatase inhibitor treatment, with 35 receiving locoregional radiotherapy. The primary outcomes included evaluation of thyroid hormones and thyroid-binding globulin post-chemotherapy, at one-year and two-year follow-ups after initiation of aromatase inhibitors. Secondary outcomes included thyroid autoantibodies and weight/body mass index.

RESULTS: There were no significant differences in thyroid parameters between the patients and healthy controls pre-chemotherapy. During treatment, free-thyroxine levels increased at both visits (p < 0.01), and total thyroxine increased at the two-year visit (p = 0.02), while triiodothyronine decreased (p < 0.01 and p = 0.03). No changes in thyroid-stimulating hormone or thyroid-binding globulin were observed, but albumin increased after one year (p < 0.01). Weight change was insignificant, and autoimmune thyroiditis prevalence was low (≤15 %). No differences in thyroid function between women with or without locoregional radiotherapy/trastuzumab were found.

CONCLUSIONS: This study suggests that, despite statistically significant changes in peripheral thyroid hormones, there were no obvious clinically important effects observed in patients with early-stage breast cancer during the two-year treatment with aromatase inhibitors. The changes were not associated with thyroid autoimmunity, non-thyroidal illness, radiotherapy, trastuzumab therapy, or high-dose corticosteroids. Further research is needed to better understand the long-term impact of aromatase inhibitors on thyroid function in this population.

CLINICAL TRIAL REGISTRATION: This study is registered at clinicaltrials.gov (NCT03784651).