Shiuan Chen

Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, CA 91010

Received 12/18/97 Accepted 7/15/98

3. AROMATASE EXPRESSION IN BREAST CANCER TISSUES

James et al. (4) reported that aromatase activity, when measured in vitro, was found to be higher in breast tumors than in the fat next to the tumor or in normal breast fat. In addition, Miller and O'Neill (5) found a highly significant correlation between aromatase activity and the presence of tumors in individual quadrants of breast tissue. Recently, using quantitative PCR analysis, adipose stromal cells surrounding the cancer cells have also been reported to contain aromatase mRNA at a higher level than adipose stromal cells in noncancerous areas (6,7). It was recently reported that the concentrations of estrogens in breast tumor tissues were found to be several-fold higher than those in plasma in postmenopausal patients (8). These results support a tumor accumulation and in situ synthesis of estrogens. In a very recent study, we detected aromatase mRNA in 67 out of 70 breast tumor specimens (9).

Immunocytochemical analysis from our laboratory first identified the presence of aromatase in breast cancer epithelial and stromal cells (10), while others had reported the presence of aromatase only in the stromal tissue (11,12). Our findings have been recently confirmed by independent in situ hybridization studies and cell proliferation assays showing that aromatase is expressed in breast cancer epithelial cells (13). Therefore, it can be stated that aromatase is expressed in breast cancer tissue, probably at a higher level than normal breast tissue, as demonstrated by enzyme activity measurement, immunocytochemistry, and RT-PCR analysis.