Tamoxifen versus high-dose oral medroxyprogesterone acetate as initial endocrine therapy for patients with metastatic breast cancer: a Piedmont Oncology Association study.

Purpose: To determine in a prospective randomized trial whether high-dose orally administered medroxy-progesterone acetate (MPA) was superior to tamoxifen in patients with recurrent or metastatic breast cancer who had received no prior endocrine therapy in either the adjuvant or advanced setting.
Patients and Methods: Patients initially received either tamoxifen 20 mg/d orally or MPA 1 g/d orally. At the time of disease progression, patients were crossed over to the other regimen. Eligibility required patients to be age > or = 18 years, performance status 0 to 3, and estrogen receptor (ER)- or progesterone receptor (PR)-positive or unknown.
Results: One hundred eighty-two eligible patients were entered and 166 were assessable for response. Complete plus partial response rates for tamoxifen and MPA were 17% and 34%, respectively (P = .01). Patients with bone metastases had a significantly higher partial response rate with MPA compared with tamoxifen (33% v 13%). Median time to treatment failure was 5.5 months for tamoxifen and 6.3 months for MPA (P = .48). The median survival duration was 24 months for tamoxifen and 33 months for MPA (P = .09). Multivariate analysis showed that treatment significantly influenced response rate, but not time to treatment failure or survival. After treatment failure following MPA, six of 42 patients (14%) treated with tamoxifen responded, compared with six of 49 (12%) treated with MPA following tamoxifen. Both agents were associated with minimal toxicity, but 35% of patients on MPA gained more than 20 lb as opposed to only 2% on tamoxifen.
Conclusion: In this trial, initial treatment with MPA of endocrine-naive metastatic breast cancer patients was associated with a significantly higher response rate but not with improvement in time to treatment failure or survival, when compared with initial treatment with tamoxifen. Further randomized trials in patients with bone metastases are warranted to determine if high-dose progestin therapy is superior to tamoxifen in these patients.