One of the most successful strategies for treating breast cancer has been the use of humanised monoclonal antibodies to target secreted growth factors or cell surface receptors whose function has been upregulated in the tumour. However, there is a need for new treatments. We have evidence to indicate that an approach that targets human growth hormone could be an effective therapeutic strategy for treating breast cancer. Growth hormone expression in human breast tumours is associated with reduced survival in patients. In addition, we have shown that inhibiting growth hormone delays tumour regrowth following radiotherapy. We aim to generate a therapeutic monoclonal antibody which inhibits the cancer promoting actions of growth hormone, for clinical applications to treat breast cancer.