Estradiol reduces resistance to AIs

Estrogen-receptor positive advanced breast cancer patients who have become resistant to endocrine therapies can derive clinical benefit from 6-mg daily doses of estradiol, according to a phase II study from St. Louis’ Washington University .

This randomized trial looked at high-dose estradiol (10 mg TID, 30 mg total) versus low-dose estradiol (2 mg TID, 6 mg total) in 66 postmenopausal women with acquired AI resistance. Patients had to have evidence of a previous response (≥ 24 weeks) to an AI or relapse occurring after two years or more of adjuvant AI treatment. If patients achieved a response or stable disease with estradiol therapy, they could be re-treated with an AI (SABCS 2008 abstract 16).

In the intent-to-treat analysis, clinical benefit was achieved by 40.7% of patients receiving 30 mg estradiol and by 41.6% of those receiving 6 mg. This included response rates of 3% and 9%, and stable disease rates of 25% and 20%, respectively.