Further molecular analyses on archived material revealed a classical HER2 insertion (p.A775_G776insYVMA) by sequencing, HER2 overexpression by immunohistochemistry (score = 2+), and HER2 amplification by dual chromogenic in situ hybridization...T-DM1 (ado-T-DM1) appeared to be the ideal choice because it has high activity in breast cancer, has excellent tolerability....Therapy with T-DM1 is ongoing without evidence of tumor progression at the time of this report.