After no additional safety signals were observed and all side effects were in line with previously reported data from previous studies and given the favorable safety profile appropriate for heavily pre-treated patients, the use of T-DM1 in second-line metastatic HER2-positive breast cancer treatment is highly recommended, both by global breast cancer treatment guidelines (ESMO, ASCO, AGO, NCCN, St. The gene discussed is ERBB2; the disease is breast cancer.