STS and breast cancer: Importantly we find STS mRNA and protein expression in both OSE and EOC cells, as well as in SKOV3 and PEO1 cell lines, confirming the potential for OSE and EOC to generate free estrogen via hydrolysis of circulating E1S. This complements evidence for estrogen generation from sulfated forms in breast cancer tissue, where sulfatase pathway is 50–200 times more active than aromatase [29].