Chemotherapy for post-menopausal women with early breast cancer seems not to result in clinically significant changes in thyroid function

OBJECTIVE: Adjuvant chemotherapy is often indicated in patients diagnosed with early breast cancer (EBC). Among others, weight gain is one of the observed side effects of both chemotherapy and other cancer treatments; however, the mechanism is not well-described. In this study, we aimed to assess thyroid function before and shortly after the course of chemotherapy for EBC.

METHODS: This is a prospective cohort study of women diagnosed with EBC. The main outcome was the thyroid function and body weight before and after completing chemotherapy. Secondary outcomes were the presence of thyroid autoantibodies and treatment radiation dosage. We included 72 patients treated with adjuvant chemotherapy, whereas 59 patients also received supraclavicular locoregional radiotherapy. Triple-negative breast cancer (BC) patients receiving chemoimmunotherapy were excluded.

RESULTS: After the chemotherapy, we observed an increase in thyroid-stimulating hormone (p = 0.03) and a decrease in free-thyroxine (p = 0.0006), with no significant weight change. The prevalence of autoimmune thyroiditis was low. On average 3 months post-chemo, we found no statistically significant difference in the thyroid function of women treated versus not treated with supraclavicular locoregional radiotherapy.

CONCLUSIONS: Although statistically significant changes in thyroid hormones were observed, this study suggests no obvious clinically significant changes in thyroid function in women with early BC after the course of chemotherapy. The decrease in thyroid function was not related to autoimmunity, non-thyroidal illness, radiotherapy, or high-dose corticosteroids. Further studies with a longer follow-up of thyroid function after adjuvant chemotherapy and supraclavicular locoregional radiotherapy are needed.