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Endocrine therapy and thyroid function in early luminal breast cancer: a controlled longitudinal retrospective
Zengwei Li1, Tingfei Song1, Yu Zhang1
1School of Clinical Medicine, Shandong Second Medical University, Weifang, Shandong, China.
Background:
Endocrine therapy is a standard treatment strategy for hormone receptor-positive breast cancer, but the long-term impact on thyroid function remains unclear. This study evaluates changes in thyroid function among patients with early luminal breast cancer receiving adjuvant endocrine therapy compared to those with benign breast disease (BBD).
Methods:
This retrospective longitudinal cohort study included 53 patients with early luminal breast cancer (BC) who received adjuvant tamoxifen (TAM) or aromatase inhibitors (AIs), and 21 BBD controls. All participants had no history of thyroid disease, chemotherapy, or radiotherapy. Thyroid function parameters (TSH, FT3, FT4) were measured at baseline, 1 year, and 3 years post-surgery. Generalized linear mixed models (GLMM) were used to compare longitudinal changes between groups.
Results:
After 3 years of endocrine therapy, the BC group showed a significant increase in TSH (from 1.92 to 3.06 μIU/mL) and decreases in FT3 (from 4.90 to 4.14 pmol/L) and FT4 (from 18.35 to 15.26 pmol/L), whereas the BBD group showed no statistically significant changes over time. Significant group-by-time interactions were found for TSH (P = 0.018), FT3 (P = 0.016), and FT4 (P < 0.001). In subgroup analysis comparing TAM and AIs, a significant interaction was observed for FT4 (P = 0.022), indicating a greater decline in FT4 with TAM, while no significant differences were found for TSH (P = 0.508) or FT3 (P = 0.204). In subgroup analysis by tumor grade, no significant time-by-grade interactions were observed for TSH (P = 0.210), FT3 (P = 0.186), or FT4 (P = 0.073).
Conclusions:
Adjuvant endocrine therapy in early luminal breast cancer was associated with statistically significant alterations in thyroid function over 3 years, characterized by increased TSH and decreased FT3 and FT4. These alterations did not differ substantially by tumor grade. However, the small sample size and the complete collinearity between treatment type and menopausal status preclude drawing independent conclusions regarding the differential effects of TAM versus AIs. Further prospective studies are warranted to validate these observations and to explore their potential clinical relevance.
