Aromatase in human common epithelial ovarian neoplasms

The expression of aromatase was evaluated in 44 ovarian carcinomas, 7 carcinomas of low malignant potential (LMP), and 14 benign adenomas. Aromatase immunoreactivity was observed in stromal cells in 35 of 44 (79.5%) ovarian carcinomas and 3 of 7 carcinomas of LMP. However, no immunoreactivity was pronounced at sites of frank invasion in ovarian carcinoma. To characterize aromatase in ovarian carcinoma, aromatase activity, mRNA expression, and alternative uses of exon 1 were determined. Quantitation of aromatase activity with the tritiated water method demonstrated 41.62 +/- 9.15 pmol/hour/mg protein in 11 ovarian carcinomas. The mean concentration of aromatase mRNA for 14 ovarian carcinomas was 3 +/- 4 amol/ng RNA, which significantly correlated with aromatase immunoreactivity. The alternative use of multiple copies of exon 1 was examined by reverse transcriptase polymerase chain reaction in 11 carcinomas. The transcript, mainly using exons 1c and 1d, was detected in 4 and 5 cases of carcinoma, respectively. Patterns of utilization of exon 1, however, did not significantly correlate with aromatase overexpression. These results suggest that aromatase is expressed in stromal cells of ovarian carcinoma but not in benign ovarian neoplasms. Increased aromatase expression in stromal cells of human ovarian carcinoma is, therefore, considered to play an important role in the biological behavior of these tumors by producing estrogens in situ as in other female sex-steroid-dependent neoplasms.