The present invention relates to an antibody, particularly a monoclonal antibody, which binds a novel epitope of the ERBB2 tyrosine kinase receptor, wherein the unique features of said binding enable interference with receptor-mediated signalling and downstream biological effects in a novel and unanticipated fashion not obtainable with state-of-the-art therapeutic antibodies. The present invention relates to compositions comprising such an antibody and its humanized derivative, as well as methods using such an antibody and derivative, particularly in ERBB2-low/non-amplified breast cancers, particularly in combination with Trastuzumab and Pertuzumab.
