SAN FRANCISCOIn a multicenter phase II trial reported at the 37th Annual Meeting of the American Society of Clinical Oncology (ASCO abstract 178), the new selective estrogen-receptor modulator (SERM) arzoxifene showed antitumor efficacy without endometrial hyperplasia in 112 patients with advanced or metastatic breast cancer.
The lead author was Aman Buzdar, MD, professor of breast medical oncology, M.D. Anderson Cancer Center.
Arzoxifene has been shown to be antagonistic in preclinical breast and endometrial models while agonistic on bone and lipids. This phase II trial evaluated the safety, toxicity, and efficacy of two dose levels (20 mg and 50 mg daily) of arzoxifene.
Patients had either tamoxifen(Drug information on tamoxifen) (Nolvadex)-sensitive disease (no prior systemic therapy or disease-free interval of at least 12 months after discontinuation of adjuvant tamoxifen) or tamoxifen-refractory disease (relapse on adjuvant tamoxifen or relapse on tamoxifen for first-line treatment of metastatic cancer).
The arms were balanced for tamoxifen sensitivity, degree of estrogen-receptor positivity, and number of metastatic sites. Patients were randomized in a double-blind design to 20 mg or 50 mg daily. Patients who progressed were given 50 mg daily or went off study.
"There are unmet needs with tam-oxifen, which is the SERM standard," said Allen S. MeLemed, MD, clinical research physician for Lilly Research Laboratories, which is developing the drug. "Particularly, there are concerns about endometrial cancer and hyperplasia. We want to see if this compound is a better SERM. Arzoxifene seems to have better preclinical efficacy than raloxifene(Drug information on raloxifene) [Evista], which is why we took this phase II study forward."
Both doses showed efficacy. The combined objective response rate for protocol-qualified patients in the tamoxifen-sensitive cohort was 19%, with a clinical benefit seen in 40% (complete response plus partial response plus stable disease). In the tamoxifen-refractory patients, the objective response rate was 9%, and clinical benefit rate was 12%.