β-catenin, when located within the nucleus, acts as an oncoprotein by activating TCF/LEF transcription factors, which in turn regulate transcription of a wide range of growth and proliferation-associated genes. Nuclear β-catenin is frequently seen in epithelial cancer cells as a result of either inappropriate Wnt signalling or inactivating mutations in genes for key β-catenin regulators or for β-catenin itself. Breast tumours are unusual, however, in that nuclear β-catenin is relatively rare in epithelial breast cancer cells. On the other hand, nuclear β-catenin expression has been documented in fibroblasts within breast fibroadenomas and benign phyllodes tumours . Preliminary observations within our laboratory indicated that stromal fibroblasts in and around breast carcinomas also frequently express nuclear β-catenin. Our aim in the present work was to validate this observation, and to determine how fibroblasts with nuclear β-catenin might influence cancer behaviour.