Catecholestrogen synthesis and metabolism by human breast tumors in vitro

The activities of enzymes which synthesize and metabolize catecholestrogens were studied in biopsy samples of human breast neoplasms. Estrogen 2-hydroxylase, a cytochrome P-450-dependent enzyme, was present in both benign and malignant neoplasms but not in normal breast tissue. Catechol O-methyltransferase activity was present in all samples examined and was significantly higher in malignant tumors [549 +/- 31 (S.E.) pmol/20 min/mg protein] than in benign neoplasms (226 +/- 41 pmol/20 min/mg protein) or in normal breast tissue (133 +/- 28 pmol/20 min/mg protein). There was no correlation, however, between estrogen 2-hydroxylase and catechol O-methyltransferase activities. The enzymes responsible for the synthesis and metabolism of catecholestrogens are present in some breast tumor specimens, suggesting that in such tissues these metabolites may be formed in vivo.