**4. Future directions**

It is becoming evident that gene expression at the site of breast cancer metastasis may not be the same as at the site of the primary tumour and we need better ways to treat metastases. It will likely be important to biopsy more metastatic tissue to provide the type of designer therapeutics aimed at pathways known to be targetable at the site of the metastasis as we currently do with the primary tumour. Currently, biopsies of metastases are rare. As stroma is known to be an active contributor to the metastasis we also need to develop therapeutic approaches aimed at targeting the stroma. The recent development of new technologies for capture and analysis of circulating tumour cells may help to improve our understanding.
