Primary endocrine therapy for advanced breast cancer: to start with tamoxifen or with medroxyprogesterone acetate?

The availability of compounds effective against metastatic disease and at the same time excellently tolerated even in long-term administration has determined the choice of tamoxifen as primary treatment for palliation in metastatic breast cancer. Other drugs or other hormonal approaches were hardly tested against tamoxifen, especially as first-line treatment.

119 patients with metastatic breast cancer and no prior endocrine therapy were randomized to receive either tamoxifen (TAM) 20 mg/day orally (64 patients), or medroxyprogesterone acetate (MAP) 1g/day i.m. 5 days/week for 4 weeks and then 500 mg twice a week (55 patients). The subsequent endocrine therapy was also prospectively defined at study entry.

A total of 111 events, contributing to the endpoint 'time to progression' have so far been observed: a study of similar size would have a 90% power to detect a hazard ratio of 1.85. Initial MAP was associated with a significantly higher remission rate (50% versus 30% for tamoxifen; p = 0.023) and a marginally significantly longer median time to progression (8.8 versus 5.4 months; p = 0.051). Overall survival was also longer for the MAP group (28 versus 20 months; p = 0.384). The use of MAP was associated with a significantly higher toxicity, mainly hypertension, weight gain and tremor.

The implications of these results are that initial endocrine therapy in postmenopausal patients with metastatic disease should be MAP if the patient is willing to accept the side effects of high-dose progestins. Progestins should be tested in the adjuvant setting for postmenopausal women, especially those with no tendency to hypertension or obesity.