Treatment of advanced breast cancer with progestins.

This paper reviews the theoretical background for the use of progestins in advanced breast cancer and the clinical experience obtained from 13 major studies. The average rate of response is about 30%, with somewhat higher rates when the dominant site of disease is localized to soft tissue and to bones, compared with viscera. Furthermore it seems that cross resistance between progestin therapy and other endocrine therapies is only partial. However, response rates related to previous therapy and to important prognostic variables such as age of the patient, disease-free interval and hormone receptor content of the tumor tissue are poorly elucidated. Only limited data are available concerning response rate in relation to dose and route of administration and data from prospective randomized trials to analyze these relations are still lacking. Considering the only modest side effects of treatment with progestins and the clinical and theoretical evidence favoring a mode of action different from that of other endocrine therapies, progestins are drugs with interesting qualities. Therefore future controlled studies with progestins alone or in combination with other systemic therapies should be carried out to establish the therapeutic efficacy of progestin therapy in primary and advanced disease.