The pattern of expression and role of triiodothyronine (T3) receptors and type I 5'-deiodinase in breast carcinomas, benign breast diseases, lactational change, and normal breast epithelium.

Aim: : To study the pattern of expression of triiodothyronine (T3) receptors and type I 5'-deiodinase in various breast pathologies comparing malignant and nonmalignant epithelia that include lactational change.

Methods And Results: A retrospective study was performed on formalin-fixed, paraffin-embedded archival material from 146 cases of carcinomas, normal breast tissue, breast tissue showing lactational change, and benign breast lesions. Archive tissue blocks were selected and sections were cut for immunohistochemistry to study the expression of thyroid hormone receptor α-1 (THR-α1) in the cytoplasm and nuclei of cells in tissues under study. Thick sections were cut for type I 5'-deiodinase evaluation using reverse transcriptional PCR.THR-α1 showed no nuclear expression in the carcinoma group. Combined nuclear and cytoplasmic expression was seen in 47.6%, 63.4%, 64.3%, and 58.3% in the benign, fibrocystic, fibroadenoma, and lactational change groups, respectively, compared with only 17.4% of cases in the carcinoma group. This suggests deregulation of the thyroid hormone in breast cancer. Theories for the possible role of thyroid hormone in the pathogenesis of breast cancer are discussed.Type I 5'-deiodinase was not shown to be differentially expressed in malignant versus nonmalignant groups.

Conclusions: Our study revealed substantial reduction in the protein expression profile of THRs in malignant versus nonmalignant mammary epithelium suggesting a possible role in breast cancer development. The presence of THRs in mammary epithelium seems to be protective against the development of breast cancer. This could serve as a potential prognostic and therapeutic target for breast cancer.