Comparison of biochemical aromatase activity with aromatase immunohistochemistry in human breast carcinomas.

The role of intratumoural aromatase in human breast cancer growth remains controversial. At the same time as the use of aromatase inhibitors in the clinical setting continues to increase, so does the need for a tool to predict the likely response to this treatment. Intratumoural aromatase is a candidate predictive marker. The presently accepted 'gold standard' methods of assessment of aromatase activity are biochemical assays. However, these are time-consuming and require relatively large amounts of fresh or frozen tissue which are frequently not available. The development of a reliable immunohistochemical technique for the assessment of intratumoural aromatase which could be applied rapidly to more readily available paraffin-embedded material is therefore highly desirable. Unfortunately aromatase immunohistochemistry is also an area of controversy; some authors describe localisation to the stromal compartment but others to the malignant epithelial cells themselves. The aim of this study was therefore to compare immunohistochemical scores using two different antibodies with biochemical aromatase activity. Taking a group of 29 human breast carcinomas we demonstrated a strong correlation between immunoreactivity with a monoclonal antibody (p = 0.01) but not with a polyclonal (p = 0.16). The monoclonal produced reactivity in both epithelial and stromal cells but the polyclonal in only stromal cells. The implications of these results are discussed together with the need for further studies.