Organ-specific homing and colonization of cancer cells are important and interesting features of metastasis. Molecular programs that contribute to this tropism may be elucidated through gene expression profiling with DNA microarrays. Using experimentally derived breast cancer cells that home specifically to bone or to lung, several investigators have concluded that distinct alterations in gene expression underlie metastasis to these sites. Minn et al. (2005) report a set of genes involved in lung-specific metastasis of breast cancer; the authors have determined the functional contribution of several genes to the metastatic cascade, as well as the relevance of these genes to human disease.