Evaluation of the thyroid and hypothyroid function after postoperative radiation therapy among breast cancer patients.

Background: The current advances in radiotherapy (RT) have improved the outcome of breast cancer (BC) patients. Despite its therapeutic benefits, the iatrogenic toxicities of RT and its impact on BC survivors are still debated, and further evaluations should be considered. This study aims to assess the rate of subclinical hypothyroidism and hypoparathyroidism among BC patients who were exposed to therapeutic radiation.

Methods: Seventy females undergoing RT for BC were enrolled in this cross-sectional study. Laboratory assessment of thyroid stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) levels was obtained to evaluate thyroid function. The parathyroid function was evaluated by measuring serum levels of Calcium (Ca), Phosphorus (P), and parathyroid hormone (PTH) at baseline, six and 12 months after RT.

Results: The mean age of patients was 54.3±6.4 years. We found no cases of hypothyroidism before radiotherapy. However, nine patients developed hypothyroidism in the six months after radiotherapy (one clinical and eight subclinical, 13% in total), and six patients were identified with hypothyroidism in the 12 months after radiotherapy (one clinical and five subclinical, 8.7% in total). Significant relationships were observed in the hypothyroidism rate at both six months (p = 0.003) and 12 months (p = 0.028) after RT compared with the baseline. There was no case of hypoparathyroidism before and after RT.

Conclusion: In summary, we found that thyroid and parathyroid dysfunction after RT are relatively common findings among women with BC. It is a treatable source of morbidity in patients undergoing RT. Therefore, routine thyroid function monitoring should be recommended to improve the quality of life in BC survivors.