These sulfo-conjugated steroids can be re-converted into active free estrogens in breast cancer tissue via cleavage of the sulfate group by the STS and further conversion by the enzymes 3β-hydroxysteroid dehydrogenase and aromatase in the case of DHEA (Santner et al., 1986; Pasqualini et al., 1997; Labrie et al., 1998; Suzuki et al., 2005; Sasano et al., 2006). This evidence concerns the gene STS and breast cancer.