Background: Estrogen is a mitogenic factor that is implicated in the genesis and progression of breast cancer via its binding to estrogen receptor (ER)-alpha. Synthesis of estrogen in situ is believed to be catalyzed mainly by aromatase. Previous studies comparing the relative contributions from tumor cells and stromal cells to local estrogen synthesis, as assessed by immunohistochemical analysis, were quite controversial and no consistent relationship was found between the presence of aromatase and any clinicopathologic factor. In addition, previous studies into aromatase gene expression and clinicopathologic factors are limited.
Methods: We assessed the level of expression of aromatase mRNA, using quantitative real-time RT-PCR, in 162 cases of invasive ductal carcinoma of the breast. Associations between aromatase expression and different clinicopathologic factors were sought.
Results: It was found that aromatase mRNA was expressed at significantly higher levels in patients older than 50 years, in those without axillary lymph node involvement, in those with tumor size less than 2 cm, and in ER-alpha positive tumors. However, no relationship was found between aromatase mRNA expression and any other clinicopathologic factor, including histologic grade and progesterone receptor status. Patients with high levels of expression of aromatase mRNA tended to have a better prognosis than did those patients with low expression.
Conclusion: These findings imply that ER-alpha and aromatase may be coexpressed in endocrine responsive patients. They may also indicate that aromatase expression could be a marker of endocrine responsiveness, and it may have prognostic implications for breast cancer progression.