A Prospective, Randomized Multicenter, Open-label Comparison of Preoperative Trastuzumab Emtansine (T-DM1) With or Without Standard Endocrine Therapy vs. Trastuzumab With Standard Endocrine Therapy Given for Twelve Weeks in Patients With Operable HER2+/HR+ Breast Cancer Within the ADAPT Protocol.

Inclusion Criteria: * Female patients, age at diagnosis 18 years and above (consider patients at 70 years and above for ADAPT Elderly) * Histologically confirmed unilateral primary invasive carcinoma of the breast * Clinical T1 - T4 (except inflammatory breast cancer) * All clinical N (cN) * No clinical evidence for distant metastasis (M0) * Known HR status and HER2 status (local pathology) Tumor block available for central pathology review * Performance Status ECOG ≤ 1 or KI ≥ 80% * Negative pregnancy test (urine or serum) within 7 days prior to start of induction treatment in premenopausal patients * Written informed consent prior to beginning specific protocol procedures, including expected cooperation of the patients for the treatment and follow-up, must be obtained and documented according to the local regulatory requirements * The patient must be accessible for treatment and follow-up Additional Inclusion criteria for participation in the HER2+/HR+ sub-protocol: * Confirmed ER and/or PR positive and HER2+ by central pathology * Clinical cT1c - T4a-c (participation of patients with tumors \>cT2 is strongly recommended) * All clinical N (participation of patients with cN0, if cT1c is strongly recommended) * Patients must qualify for neoadjuvant treatment * LVEF \> 50%; LVEF within normal limits of each institution measured by echocardiography and normal ECG (within 42 days prior to induction treatment) Exclusion Criteria: * Known hypersensitivity reaction to the compounds or incorporated substances * Prior malignancy with a disease-free survival of \< 10 years, except curatively treated basalioma of the skin, pTis of the cervix uteri * Non-operable breast cancer including inflammatory breast cancer * Previous or concurrent treatment with cytotoxic agents for any reason after consultation with the sponsor * Concurrent treatment with other experimental drugs. Participation in another clinical trial with any investigational not marketed drug within 30 days prior to study entry * Male breast cancer * Concurrent pregnancy; patients of childbearing potential must implement * a highly effective (less than 1% failure rate) non-hormonal contraceptive measures during the study treatment * Breast feeding woman * Sequential breast cancer * Reasons indicating risk of poor compliance Patient not able to consent Additional Exclusion Criteria for participation in the HER2+/HR+ sub-protocol: * Known polyneuropathy ≥ grade 2 * Severe and relevant co-morbidity that would interact with the application of cytotoxic agents or the participation in the study * Inadequate organ function (e.g. hepatic impairment, pulmonary disease, etc.) * Uncompensated cardiac function (current unstable ventricular arrhythmia * requiring treatment, history of symptomatic CHF NYHA classes II-IV), history of myocardial infarction or unstable angina pectoris within 6 months of enrollment, history of severe hypertension, CAD - coronary artery disease) * Severe dyspnea * Pneumonitis Abnormal blood values: * Thrombocytopenia \> CTCAE grade 1 * Increases in ALT/AST \> CTCAE grade 1 * Hypokalaemia \> CTCAE grade 1 * Neutropenia \> CTCAE grade 1 * Anaemia \> CTCAE grade 1