A STUDY OF THE EFFICACY AND SAFETY OF TRASTUZUMAB EMTANSINE (TRASTUZUMAB-MCC-DM1) VS. TRASTUZUMAB (HERCEPTIN®) AND DOCETAXEL (TAXOTERE®) IN PATIENTS WITH METASTATIC HER2-POSITIVE BREAST CANCER WHO HAVE NOT RECEIVED PRIOR CHEMOTHERAPY FOR METASTATIC DISEASE: