Thyroid hormones, silencing mediator for retinoid and thyroid receptors and prognosis in primary breast cancer

Background/Aim: Silencing mediator of retinoid and thyroid receptors (SMRT) is a nuclear corepressor in thyroid and estrogen hormones pathways. The aim was to evaluate SMRT expression in relation to thyroid hormone levels and prognostic markers in breast cancer (BC). Patients and Methods: Serum and tumor tissues were obtained from 36 patients with benign breast disease (BBD) and 79 BC patients. SMRT expression was determined by immunohistochemistry. Free-triiodothyronine (FT3), free thyroxine (FT4) and thyroid-stimulating hormone (TSH) were measured in serum. Results: Higher FT4, lower FT3/FT4 ratio and higher expression of SMRT were found in BC compared to BBD (for all p<0.001). In BC, increased SMRT expression was associated with lower FT3 (p=0.028), higher tumor grade (p=0.031), increased KI67 proliferation index (p=0.015), higher risk of recurrence (p=0.014) and shorter disease-free survival (p=0.006). In multivariate analysis, SMRT overexpression and below-median levels of TSH were independent prognostic factors in BC. Conclusion: Elevated FT4 and decreased FT3/FT4 in BC patients suggest a role for thyroid hormones in malignant transformation. SMRT tumor overexpression is associated with lower FT3 levels, tumor proliferative activity and an aggressive clinical course.