A Phase Ii Study To Assess The Safety And Efficacy Of The Steroid Sulfatase Inhibitor Irosustat When Added To An Aromatase Inhibitor In Er Positive Locally Advanced Or Metastatic Breast Cancer Patients (Iris) - Trial Results.

549Background: Lowering estradiol levels is a key treatment modality for estrogen-receptor positive (ER+) postmenopausal breast cancer (BC).Currently, only one of the two main enzymes for oestrogen biosynthesis is targeted therapeutically in BC, namely aromatase, with the second pathway steroid sulfatase (STS) yet to be exploited. Irosustat, is a first generation, orally active, irreversible steroid sulfatase (STS) inhibitor. We performed a multicentre, open label phase II trial of the addition of Irosustat to first-line aromatase inhibitor (AI) in patients (pts) with advanced BC to test the hypothesis that the addition of Irosustat to AI may result in clinical benefit. Methods: Postmenopausal women with ER+ locally advanced or metastatic breast cancer who had derived clinical benefit from a first line AI and who subsequently progressed were enrolled. The first line AI was continued and Irosustat (40mg orally daily) added. The primary endpoint was clinical benefit rate (CBR, as defined by SD, CR or PR for...