CYP19A1 and endometriosis: However, Purohit et al. reported that STS activity in peritoneal ectopic implants and matched eutopic endometrium was higher than aromatase activity, which thus suggested that the STS pathway is important in estrogen formation and that STS inhibitors might be useful for treatment of endometriosis (Purohit et al., 2008; Delvoux et al., 2009).