Ribociclib in Hormone Receptor-positive, HER2-negative Early Breast Cancer With Residual Disease After Neoadjuvant Chemotherapy

Inclusion Criteria: * Willingness for study participation with written informed consent * Female with age at least 18 years * Histologically confirmed unilateral or bilateral primary invasive breast cancer * Residual invasive disease post-neoadjuvant either in the breast or as residual nodal invasion * Histologically confirmed hormone receptor-positive (≥1% ER and/or PR positive stained cells) and HER2-negative (IHC 2+ with FISH-negative or IHC 0-1+) assessed preferably on core biopsy of the breast or tissue from post-neoadjuvant residual invasive disease, or if no other tissue is available the residual tumor of the lymph node can be assessed. In case of bilateral breast cancer, tumor tissue of both sides needs to be assessable * Histologically confirmed Ki67 expression assessed preferably on core biopsy or post-neoadjuvant residual invasive disease of the breast, or if not possible, of residual nodal invasion. In case of bilateral breast cancer, tumor tissue of both sides needs to be assessable * QTc interval \< 450 msec with mean resting heart rate 50-99 beats/min (determined by ECG) * Patients must have received neoadjuvant chemotherapy of at least 18 weeks. This period must include 6 weeks of a taxane-containing neoadjuvant therapy (Exception: For patients with progressive disease that occurred after at least 6 weeks of taxane-containing neoadjuvant treatment, a total treatment period of less than 18 weeks is also eligible) * Adequate surgical treatment including resecti…