The calendar, the expected date of completion, the inclusion and exclusion criteria of the trial were changed, reducing the number of stratification and updating the list of Participating Sites. Collaboration in the study of the German Breast Group (GBG –German Breast Group) that will be sponsor of the study in German sites is also included in this modification.

Creation of an Independent Data Monitoring Committee. Statistical Clarifications. Correction of previous errata: Proteinuria algorithm. Update of participating sites.

A new drug, Fulvestrant, that belongs to the same type of endocrine treatment has been incorporated. Now patients who were previously treated with aromatase inhibitor can be recruited. As a result of this change, the study title has been modified. The 12-month washing period is eliminated in the inclusion criterion # 12 in the case of having previously received aromatase inhibitor, since in this amendment the option is given to start treatment in combination or as a single agent with fulvestrant, not being necessary this temporary margin. Corrections have been made, corrected errata and terms have been modified or clarified throughout the protocol, as well as the update of the participating sites and staff of the study involved. In the informed consent of the study, the main adverse events known from the use of fulvestrant are included, as well as those already indicated of letrozole.