The present application describes an isolated antibody or a fragment, variant or derivative thereof / capable of specifically binding to Her2/neu comprising a heavy chain variable domain wherein said heavy chain variable domain comprises an amino acid sequence as set out in at least one of SEQ ID NOs: 1, 2 or 3 or a sequence having at least 75% identity (homology) thereto or a functional fragment thereof as well as nucleic acid sequences encoding the same and methods for their production. The application also relates to a method for the treatment of Her2/neu expressing cancer in a patient comprising administering to the patient in need of such treatment a therapeutically effective amount of any of those antibody, polypeptide or nucleic acid molecules described herein.