The primary study endpoint is objective response rate. The study has been designed following Simon's test, with a p1-p0=0.15. p1 is the optimum level of activity of the experimental treatment (exemestane), and p0 is the minimum expected activity. In this study, p1 is 25% (25% of RR) and p0 is 10% (10% of RR). With an alpha error of 0.05 and a beta error of 0.1, Simon test establishes a first step of 21 patients per treatment arm. If at least 2 objective responses are observed in exemestane arm, recruitment will continue until 100 patients have been recruited. After this second recruitment phase, at least 7 objective responses must be observed to confirm the expected exemestane level of activity.