Profile of thyroid hormones in breast cancer patients

Prospectively measured triiodothyronine levels are positively associated with breast cancer risk in postmenopausal women

Introduction

The potential association between hypo- and hyperthyroid disorders and breast cancer has been investigated in a large number of studies during the last decades without conclusive results. This prospective cohort study investigated prediagnostic levels of thyrotropin (TSH) and triiodothyronine (T3) in relation to breast cancer incidence in pre- and postmenopausal women.

Methods

In the Malmö Preventive Project, 2,696 women had T3 and/or TSH levels measured at baseline. During a mean follow-up of 19.3 years, 173 incident breast cancer cases were retrieved using record linkage with The Swedish Cancer Registry. Quartile cut-points for T3 and TSH were based on the distribution among all women in the study cohort. A Cox's proportional hazards analysis was used to estimate relative risks (RR), with a confidence interval (CI) of 95%. Trends over quartiles of T3 and TSH were calculated considering a P-value < 0.05 as statistically significant. All analyses were repeated for pre- and peri/postmenopausal women separately.

Results

Overall there was a statistically significant association between T3 and breast cancer risk, the adjusted RR in the fourth quartile, as compared to the first, was 1.87 (1.12 to 3.14). In postmenopausal women the RRs for the second, third and fourth quartiles, as compared to the first, were 3.26 (0.96 to 11.1), 5.53 (1.65 to 18.6) and 6.87 (2.09 to 22.6), (P-trend: < 0.001). There were no such associations in pre-menopausal women, and no statistically significant interaction between T3 and menopausal status. Also, no statistically significant association was seen between serum TSH and breast cancer.

Conclusions

This is the first prospective study on T3 levels in relation to breast cancer risk. T3 levels in postmenopausal women were positively associated with the risk of breast cancer in a dose-response manner.

Aberrant methylation of the THRB gene in tissue and plasma of breast cancer patients

The thyroid hormone receptors (TR) have three major isoforms, TRalpha1, TRalpha2, and TRbeta1; these are ligand-dependent nuclear transcription factors. THRB, the gene encoding TRbeta1, is considered a potential cancer suppressor. The mechanism of its inactivation is not yet clear. Aberrant silencing of THRB in breast cancer tissue and plasma by promoter hypermethylation was investigated in the present study. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to examine THRB mRNA expression in the breast cancer tissues. Methylation-specific polymerase chain reaction (MSP) combined with nested PCR was used to determine the methylation status of the THRB gene promoter region in 40 cancer tissue and 40 plasma samples from breast cancer patients. Methylation status of MSP product in plasma was also evaluated by direct sequencing. The expression of THRB mRNA in breast cancer tissues was lower than that in the normal tissues; hypermethylation was found in 32 of 40 breast cancer tissues (80%) and in 28 of 40 plasma samples (70%). Loss of THRB gene expression was associated with the CpG island hypermethylation of promoter regions. THRB gene CpG island methylation was not related to clinical pathologic parameters. Sequencing results were identical to agarose gel electrophoresis results. The present results indicate that hypermethylation of THRB as an alternative gene silencing mechanism is highly prevalent in breast cancer. Methylated tumor-specific DNA may serve as a plasma biomarker for prognosis in patients with breast cancer.

Prevalence of hypothyroidism in benign breast disorders and effect of thyroxine replacement on the clinical outcome

BACKGROUND

The aim of this study was to determine the prevalence of hypothyroidism in patients with benign breast disorders (BBD). We then asked if thyroxine replacement in hypothyroid patients has any impact on the clinical outcome of the BBD.

METHODS

This prospective study included 201 women with BBD. None of the included patients had previously suspected hypothyroidism. Clinical, laboratory, and follow-up details of the patients were noted. Baseline serum thyroxine, thyroid-stimulating hormone (TSH), and prolactin estimation was done in all cases. Thyroid peroxidase antibody (TPOAb) estimation was done in hypothyroid patients and/or patients with a goiter. In addition to the standard conservative management protocol, hypothyroid patients were given thyroxine replacement therapy. Their response to treatment was assessed at 3-month intervals. The clinical outcomes of euthyroid and hypothyroid groups were compared.

RESULTS

The mean age of the patients was 34 +/- 8 years, and the mean length of follow-up was 13.0 +/- 4.2 months. The overall prevalence of hypothyroidism was 23.2% (nipple discharge 37%, mastalgia 23%, lump/lumpiness 17.4%). The rate of hypothyroidism and the mean serum TSH concentration were significantly higher among patients with nipple discharge than among those with mastalgia (P = 0.001) or a lump (P = 0.01). In all, 39% of hypothyroid women had TSH concentrations >10 mIU/l, and 53% had an elevated TPOAb titer. BBD symptoms were alleviated in 83% of the hypothyroid patients with only thyroxine replacement. The final clinical outcomes of hypothyroid patients with nipple discharge and mastalgia were significantly better than that of their euthyroid counterparts (P = 0.028 and 0.001, respectively); no significant difference was noted in patients with lumpiness (P = 0.144).

CONCLUSIONS

All women with BBD should be screened for hypothyroidism because the prevalence of hypothyroidism is high among this group and correction of hypothyroidism results in significant clinical improvement of BBD in most of these patients.

Effects of thyroid hormones on human breast cancer cell proliferation

The involvement of estrogens in breast cancer development and growth has been well established. However, the effects of thyroid hormones and their combined effects with estrogens are not well studied. We investigated the response of human breast cancer cells to thyroid hormone, particularly the role of T3 in mediating cell proliferation and gene expression. We demonstrated that 17beta-estradiol (E2) or triiodothyronine (T3) promoted cell proliferation in a dose-dependent manner in both MCF-7 and T47-D cell lines. The E2- or T3-dependent cell proliferation was suppressed by co-administration of the ER antagonist ICI. We also demonstrated that T3 could enhance the effect of E2 on cell proliferation in T47-D cells. Using an estrogen response element (ERE)-mediated luciferase assay, we determined that T3 was able to induce the activation of ERE-mediated gene expression in MCF-7 cells, although the effects were much weaker than that induced by E2. These results suggest that T3 can promote breast cancer cell proliferation and increase the effect of E2 on cell proliferation in some breast cancer cell lines and thus that T3 may play a role in breast cancer development and progression.

Influence of thyroid hormone receptors on breast cancer cell proliferation

BACKGROUND

The involvement of thyroid hormones in the development and differentiation of normal breast tissue has been established. However, the association between breast cancer and these hormones is controversial. Therefore, the objective of the present study was to determine the protein expression pattern of thyroid hormone receptors in different human breast pathologies and to evaluate their possible relationship with cellular proliferation.

PATIENTS AND METHODS

The presence of thyroid hormone receptors was evaluated by immunohistochemistry and western blot analysis in 84 breast samples that included 12 cases of benign proliferative diseases, 20 carcinomas in situ and 52 infiltrative carcinomas.

RESULTS

TR-alpha was detected in the nuclei of epithelial cells from normal breast ducts and acini, while in any pathological type this receptor was located in the cytoplasm. However, TR-beta presented a nuclear location in benign proliferative diseases and carcinomas in situ and a cytoplasmatic location in normal breast and infiltrative carcinomas. The highest proliferation index was observed in carcinomas in situ, although in infiltrative carcinomas an inverse correlation between this index and the TR-alpha expression was encountered.

CONCLUSIONS

The results of this study reveal substantial changes in the expression profile of thyroid hormone receptors suggesting a possible deregulation that could trigger breast cancer development.