This was the first trial to directly compare ado-trastuzumab emtansine with astandard trastuzumab plus chemotherapy regimen in patients who had not received treatment for metastatic disease.In this trial, 137 patients with advanced HER2-positive breast cancer were randomized in a 1:1 ratio to receive ado-trastuzumab emtansine 3.6 mg/kg IV once every 3 weeks vs. trastuzumab 8 mg/kg loading dose then 6 mg/kg IV anddocetaxel 75 or 100 mg/m2 (HT) at the investigator’s discretion, once every 3 weeks. This evidence concerns the gene ERBB2 and breast cancer.