In order to study acquired resistance to Trastuzumab (Tz), we performed 3D cell cultures from two HER2+ human breast adenocarcinoma cell lines: Tz-sensitive BT-474 and Tz-resistant BT-474 (BT-474R), which were obtained by chronic exposure to this antibody [17]. This evidence concerns the gene ERBB2 and breast adenocarcinoma.