Phase I trial of droloxifene in patients with metastatic breast cancer.

Droloxifene (3-hydroxytamoxifen) is a new, nonsteroidal antiestrogen. In comparison with tamoxifen, it has a 10- to 64-fold higher affinity for the estrogen receptor and has shown a lower estrogenic and higher antiestrogenic effect in experimental studies. The objective of this study was to determine the toxicity (and its reversibility) of droloxifene given at different doses to patients with advanced metastatic breast cancer refractory to conventional endocrine therapy and chemotherapy. In this study, 30 patients were treated in groups of 6 at 5 different doses (20, 40, 100, 200, and 300 mg) by mouth once a day. Toxic effects included hot flashes, nausea, and fatigue and were not dose-related. Toxicity did not require any dose reduction or discontinuation of therapy. There was one episode of deep venous thrombosis and pulmonary embolism. There was no complete or partial response in this study, but four patients showed a minor response (13%). These data illustrate that this drug is well tolerated and needs to be further evaluated in phase II and III studies.