January 2008 Clinical Trial Reports

By Stanton R. Mehr
Published: Thursday, Jun 24, 2010

Atamestane Plus Toremifene Compared With Letrozole for Advanced Receptor-Positive Breast Cancer Treatment

A phase III double-blind trial was recently conducted in 60 centers in the United States, Russia, Ukraine, and Canada to compare the efficacy of the steroidal aromatase inhibitor atamestane (ATA) used with toremifene (TOR) to obtain complete estrogen blockage versus the nonsteroidal aromatase inhibitor letrozole (LET) in postmenopausal women with receptor-positive advanced breast cancer.

The primary endpoint in the study was time to progression, and the secondary objectives included overall survival, objective response, and time to treatment failure.

The researchers included postmenopausal patients with receptor-positive advanced breast cancer who had completed adjuvant hormonal therapy more than one year before enrollment. Four hundred thirty-four patients were randomly assigned to receive treatment with daily ATA 500 mg with TOR 60 mg, and 431 were assigned to receive LET 2.5 mg.

The investigators revealed that the time to progression of disease was 11.2 months in both groups. The median times to treatment failure were not statistically different (ATA TOR, 9.24 mo vs. LET, 10.44 mo). The mean hazard ratios were 1.00 for time to progression, 0.99 for time to treatment failure, and 0.98 for overall survival. The frequency of objective responses was slightly greater in the LET group (ATA TOR group, 30% vs. LET, 36%). Adverse events were similar in both groups, with serious adverse events experienced in 10% of the ATA TOR group and 11% in the LET group.

The researchers concluded that time to progression was identical in both treatment groups of postmenopausal women, and believe that this regimen represents the first endocrine therapy that is comparable with LET in advanced breast cancer. The efficacy of the aromatase inhibitor was not decreased by adding an antiestrogen, they added, unlike that seen in a previous major trial (the Anastrozole, Tamoxifen, and Combined trial). They believe that these results warrant further investigation of aromatase inhibitors with highly selective estrogen-receptor modulators.

Mean Hazard Ratios For The Two Treatment Regimens.

ATA = Atamestane, TOR = toremifene, LET = letrozole.

Criteria ATA TOR LET
Time to Progression 1.00 0.99
Time to Treatment Failure 1.00 0.99
Overall Survival 1.00 0.98

Goss P, Bondarenko, IN, Manikhas GN, et al: Phase III, double-blind, controlled trial of atamestane plus toremifene compared with letrozole in postmenopausal women with advanced receptor-positive breast cancer. J Clin Oncology 2007;25:4961-4966.


Tamoxifen Superior to Arzoxifene for Locally Advanced or Metastatic Breast Cancer

Arzoxifene is an investigational selective estrogen receptor modulator, which, according to animal models, is more potent than raloxifene in preventing mammary cancer. Researchers from Bangalore, India, sought to test the efficacy of arzoxifene compared with tamoxifen for treating locally advanced or metastatic breast cancer.

The study group comprised women with estrogen- or progesterone-receptor–positive breast cancer who had not received previous systemic therapy, or those who had relapsed more than 12 months after adjuvant hormonal therapy was stopped. They were randomly assigned to receive arzoxifene 20 mg or tamoxifen 20 mg daily. The primary endpoint was progression-free survival. Secondary end points included tumor response, safety, and overall survival.

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