STS and ovarian cancer: The importance of the local formation of E2 via the sulfatase pathway is supported by high levels of STS and significantly down-regulated SULT1E1 together with metabolism of E1-S to E1 (Milewich and Porter, 1987; Chura et al., 2009a) and E2 (Ren et al., 2015) in tissue samples and model cell lines of ovarian cancer.