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The aim of this study was to investigate the expression of thyroid hormone receptor &#946;1 (THR&#946;1) by immunohistochemistry in breast cancer (BC) tissues and to correlate the results with clinico-biological parameters. In a well-characterized cohort of 274 primary BC patients, THR&#946;1 was widely expressed with a predominant nuclear location, although cytoplasmic staining was also frequently observed. Both nuclear and cytoplasmic THR&#946;1 were correlated with high-risk BC markers such as human epidermal growth factor receptor 2 (HER2), Ki67 (also known as MKI67), prominin-1 (CD133), and N-cadherin. Overall survival analysis demonstrated that cytoplasmic THR&#946;1 was correlated with favourable survival (<i>p</i> = 0.015), whereas nuclear THR&#946;1 had a statistically significant correlation with poor outcome (<i>p</i> = 0.038). Interestingly, in our cohort, nuclear and cytoplasmic THR&#946;1 appeared to be independent markers either for poor (<i>p</i> = 0.0004) or for good (<i>p</i> = 0.048) prognosis, respectively. Altogether, these data indicate that the subcellular expression of THR&#946;1 may play an important role in oncogenesis. Moreover, the expression of nuclear THR&#946;1 is a negative outcome marker, which may help to identify high-risk BC subgroups.