Abstract: The invention relates to the use of an antibody or a fragment thereof, specific against substance P, for the manufacture of a medicament for therapeutic treatment of a cancer expressing NK1 receptor and/or a ErbB receptor family member (i.e. the epidermal growth factor receptors family), by direct administration to a mammal, including a human. The administration of an antibody against substance P to a panel of breast cancer cell lines, inhibits HER2 activation and expression, causing a downregulation of different genes involved in cell cycle progression, like cyclin D1, cyclin E, cdk4 and cdk2. A decrease in proliferation and an arrest in G1 phase of cell cycle are observed. On the other hand, the antibody causes an induction of apoptosis.