The role of STS and OATP-B mRNA expression in predicting the clinical outcome in human breast cancer

Abstract

Background: Steroid sulfatase (STS) is the enzyme responsible for hydrolysing biologically inactive estrogen sulfates to active estrogens. Therefore it plays a significant role in supporting the growth of hormone-dependent tumours of the breast, endometrium and prostate. OATP-B is a member of a family of membrane transporter proteins that regulates the uptake of steroid sulfates through cell membranes. Our objective was to determine, using quantitative PCRA whether the mRNA expression levels from these genes were positively correlated with clinical outcome in human breast cancer. This is the first study in the literature to examine the relationship between STS and OATP-B in human breast cancer and to investigate the potential prognostic value of OATP-B.

Materials and methods: A total of 153 samples (120 tumour tissues and 33 normal breast tissues) were analysed. The levels of transcription of STS and OATP-B were determined using real-time quantitative PCR and normalized against cytokeratin 19. The levels of expression were analysed against tumour's stage, grade, nodal status, local relapse, distant metastasis, ERalpha, ERbeta and HER1-4 receptor status and survival over a 10 year follow up period.

Results: The levels of STS mRNA were significantly higher in malignant samples (p=0.031) and in node positive disease (p=0.0222). STS mRNA expression increased with increasing tumour grade but this did not reach statistical significance. A significant increase was also noted in levels correlating with tumour stage when stages TNM1 and TNM2, TNM2 and TNM3, and TNM3 and TNM4 (p=0.00001, 0.0017 and 0.02, respectively) were compared. Furthermore, STS expression levels positively correlated with progression of disease, as levels were significantly higher in samples from patients who developed metastasis, local recurrence, or died of breast cancer when compared to those who were disease free for >10 years (p=0.0036). No significant correlation was found between the levels of STS expression and ERalpha/ERbeta/ status. The levels positively correlated with HER1 and HER3 receptors. The levels of mRNA expression of OATP-B were higher in malignant tissue compared to normal tissue; this, however, did not reach statistical significance (p=0.4045). Levels were also higher in node positive disease (p=0.0672). Expression levels increased with increasing tumour grade and this became statistically significant when comparing grade 1 to 2, and grade 2 to 3 (p=0.0271 and 0.0289, respectively). An increase in levels correlating with TNM tumour staging was also observed; this, however, did not reach statistical significance. There was no significant correlation between OATP-B expression levels and clinical progression of breast cancer. No correlation was found between STS and OATP-B expression levels.

Conclusion: This study demonstrates a compelling trend for STS transcription levels to be higher in cancer tissues and in patients who developed progressive disease. OATP-B expression levels correlated with the grade and stage of the disease, but not with the clinical outcome. These results suggest that STS mRNA has a significant potential as an important predictor of clinical outcome in patients with breast cancer.