A bispecific anti-HER2 antibody comprising a first immunoglobulin antigen-binding domain and a second immunoglobulin antigen-binding domain, and comprising a first and a second polypeptide chain associated with each other, wherein: (i) the first immunoglobulin antigen-binding domain comprises a heavy chain variable region and a light chain variable region comprising: (a) a variable heavy chain CDR-1 (VH-CDR1) identical to SEQ ID NO: 1; (b) a variable heavy chain CDR-2 (VH-CDR2) identical to SEQ ID NO: 2; (c) a variable heavy chain CDR-3 (VH-CDR3) identical to SEQ ID NO: 3; (d) a variable light chain CDR-1 (VL-CDR1) identical to SEQ ID NO: 4; (e) a variable light chain CDR-2 (VL-CDR2) identical to SEQ ID NO: 5; and, (f) a variable light chain CDR-3 (VL-CDR3) identical to SEQ ID NO: 6; and (ii) the second immunoglobulin antigen-binding domain comprises a scFv comprising: (g) a VH-CDR1 comprising the amino acids of SEQ ID NO:54; (h) a VH-CDR2 comprising the amino acids of SEQ ID NO:55; (i) a VH-CDR3 comprising the amino acids of SEQ ID NO:56; (j) a VL-CDR1 comprising the amino acids of SEQ ID NO:57; (k) a VL-CDR2 comprising the amino acids of SEQ ID NO:58; and a VL-CDR3 comprising the amino acids of SEQ ID NO:59; and wherein: (a) the first polypeptide chain is selected from: [TZ S]-[L 1]-[ B VH]-[ B CH]-[Fc x] [ B VH]-[ B CH]-[Fc x]-[L 2]-[TZ S] [ B VH]-[ B CH]-[L 3]-[TZ S]-[L 4]-[Fc x] and (b) the second polypeptide chain comprises [ B VL]-, wherein: - TZs is an scFv that binds the same epitope as trastuzumab; - B VH, B VL and B CH are the VH, VL and CH1 regions, respectively, of an antibody capable of binding to an HER2 epitope distinct from the epitope recognized by the trastuzumab antibody; - CL is a human kappa or a human lambda IgG light chain constant region; - L 1, L 2, L 3, and L 4 are peptide linkers; - Fc x is an Fc domain; and wherein: - B VH comprises a VH-CDR1, a VH-CDR2, and a VH-CDR3 identical to SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3, respectively; - B VL comprises a VL-CDR1, aVL-CDR2, and a VL-CDR3 identical to SEQ ID NO: 4, SEQ ID NO: 5, and SEQ ID NO: 6, respectively; - [TZs] comprises a VH-CDR1, a VH-CDR2, and a VH-CDR3 comprising the amino acids of SEQ ID NO: 54, SEQ ID NO: 55, and SEQ ID NO: 56, respectively; and a VL-CDR1, a VL-CDR2, and a VL-CDR3 comprising the amino acids of SEQ ID NO: 57, SEQ ID NO: 58, and SEQ ID NO: 59, respectively. (i) the first immunoglobulin antigen-binding domain comprises a heavy chain variable region and a light chain variable region comprising: (a) a variable heavy chain CDR-1 (VH-CDR1) identical to SEQ ID NO: 1; (b) a variable heavy chain CDR-2 (VH-CDR2) identical to SEQ ID NO: 2; (c) a variable heavy chain CDR-3 (VH-CDR3) identical to SEQ ID NO: 3; (d) a variable light chain CDR-1 (VL-CDR1) identical to SEQ ID NO: 4; (e) a variable light chain CDR-2 (VL-CDR2) identical to SEQ ID NO: 5; and, (f) a variable light chain CDR-3 (VL-CDR3) identical to SEQ ID NO: 6; and (a) a variable heavy chain CDR-1 (VH-CDR1) identical to SEQ ID NO: 1; (b) a variable heavy chain CDR-2 (VH-CDR2) identical to SEQ ID NO: 2; (c) a variable heavy chain CDR-3 (VH-CDR3) identical to SEQ ID NO: 3; (d) a variable light chain CDR-1 (VL-CDR1) identical to SEQ ID NO: 4; (e) a variable light chain CDR-2 (VL-CDR2) identical to SEQ ID NO: 5; and, (f) a variable light chain CDR-3 (VL-CDR3) identical to SEQ ID NO: 6; and (ii) the second immunoglobulin antigen-binding domain comprises a scFv comprising: (g) a VH-CDR1 comprising the amino acids of SEQ ID NO:54; (h) a VH-CDR2 comprising the amino acids of SEQ ID NO:55; (i) a VH-CDR3 comprising the amino acids of SEQ ID NO:56; (j) a VL-CDR1 comprising the amino acids of SEQ ID NO:57; (k) a VL-CDR2 comprising the amino acids of SEQ ID NO:58; and a VL-CDR3 comprising the amino acids of SEQ ID NO:59; (g) a VH-CDR1 comprising the amino acids of SEQ ID NO:54; (h) a VH-CDR2 comprising the amino acids of SEQ ID NO:55; (i) a VH-CDR3 comprising the amino acids of SEQ ID NO:56; (j) a VL-CDR1 comprising the amino acids of SEQ ID NO:57; (k) a VL-CDR2 comprising the amino acids of SEQ ID NO:58; and a VL-CDR3 comprising the amino acids of SEQ ID NO:59; a VL-CDR3 comprising the amino acids of SEQ ID NO:59; (a) the first polypeptide chain is selected from: [TZ S]-[L 1]-[ B VH]-[ B CH]-[Fc x] [ B VH]-[ B CH]-[Fc x]-[L 2]-[TZ S] [ B VH]-[ B CH]-[L 3]-[TZ S]-[L 4]-[Fc x] and [TZ S]-[L 1]-[ B VH]-[ B CH]-[Fc x] [ B VH]-[ B CH]-[Fc x]-[L 2]-[TZ S] [ B VH]-[ B CH]-[L 3]-[TZ S]-[L 4]-[Fc x] and (b) the second polypeptide chain comprises [ B VL]-, - TZs is an scFv that binds the same epitope as trastuzumab; - B VH, B VL and B CH are the VH, VL and CH1 regions, respectively, of an antibody capable of binding to an HER2 epitope distinct from the epitope recognized by the trastuzumab antibody; - CL is a human kappa or a human lambda IgG light chain constant region; - L 1, L 2, L 3, and L 4 are peptide linkers; - Fc x is an Fc domain; - B VH comprises a VH-CDR1, a VH-CDR2, and a VH-CDR3 identical to SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3, respectively; - B VL comprises a VL-CDR1, aVL-CDR2, and a VL-CDR3 identical to SEQ ID NO: 4, SEQ ID NO: 5, and SEQ ID NO: 6, respectively; - [TZs] comprises a VH-CDR1, a VH-CDR2, and a VH-CDR3 comprising the amino acids of SEQ ID NO: 54, SEQ ID NO: 55, and SEQ ID NO: 56, respectively; and a VL-CDR1, a VL-CDR2, and a VL-CDR3 comprising the amino acids of SEQ ID NO: 57, SEQ ID NO: 58, and SEQ ID NO: 59, respectively.