The aim of this study was to detect and analyze changes in hormone receptor (HR) status after treatment of operable breast cancer with neoadjuvant chemotherapy (NCT). Patients were treated from 1982 to 2004 with different NCT combinations, mainly in successive prospective phase II trials. HR status before and after NCT was retested and reviewed in a blinded fashion by two pathologists, for 420 patients from a database of 710 patients. Among these 420 tumors, 145 (35%) were HR negative and 275 (65%) were HR positive before NCT. The HR status had changed after treatment in 98 patients (23%): 61 patients (42%) initially HR negative became HR positive. This HR-positive switch was significantly correlated with better overall survival (OS), compared with patients with unchanged HR-negative tumors. Moreover, this HR-positive switch also had an effect on disease-free survival (DFS). Conversely, 37 patients (13%) initially HR positive became HR negative after NCT. However, this group of previously positive patients still had a survival advantage for OS, but not for DFS. The Allred score was evaluated before and after chemotherapy. An increase in Allred score after NCT was significantly correlated with better DFS but not OS. It was previously shown, for other tumor parameters, that residual disease after NCT, rather than parameters evaluated on the initial biopsy, must be considered for patient prognosis. In this work, NCT induced variations in HR status in 23% of patients. A positive switch in HR status after NCT could be an indicator of better prognosis for patient outcome.