Inhibitors of the enzyme farnesyl protein transferase prevent a key step in the post-translational processing of the Ras protein, and were developed initially as a therapeutic strategy to inhibit cell signalling in ras-transformed cells. As more has been learnt about the biological effects of farnesyl transferase inhibitors (FTIs) on cancer cells, it is clear that tumours without oncogenic ras mutations such as breast cancer may also be targets for FTI therapy. This article reviews the rationale for the development of FTIs, focussing on early preclinical data in breast cancer models together with preliminary results from the first phase II study of an FTI in advanced breast cancer.