While there have been significant improvements in breast cancer therapy over the last few decades, the fact that metastatic breast cancer remains incurable as well as the finding that adjuvant therapy reduces the breast cancer death hazard ratio by about 30% only underlines the need for novel therapeutic strategies. Currently, there is much interest in 'targeting therapy' for different malignancies. The majority of breast cancers harbour the insulin-like growth factor (IGF)-1 receptor, and IGF-1 has been found to be one of the most potent mitogens to breast cancer cells in vitro. Recent findings that the level of IGF-1 predicts subsequent risk of breast cancer in premenopausal patients further underlines the potential biological importance of this growth factor to the disease. While endocrine treatment with anti-oestrogens as well as progestins have been found to interact with the IGF system in vivo, the extent of these effects on antitumour action remains poorly understood. This paper discusses current strategies and results aiming at targeting IGF-1 as therapy for breast cancer.