We used Affymetrix microarrays to compare gene expression profiles of the metastatic parental breast cancer cell line MDA-MB-435 (435) and the non-metastatic daughter cell line created by the stable expression of the BReast cancer Metastasis Suppressor 1 (BRMS1) gene in 435 cells, MDA-MB-435-BRMS1 (435/BRMS1). Analysis of microarray data provided insight into some of the potential mechanisms by which BRMS1 inhibits tumor formation at secondary sites. Furthermore, due to the importance of the microenvironment, we also examined gene expression under different growth conditions (i.e., plus or minus serum). Expression of 565 genes was significantly (adjusted P-value <0.05) altered regardless of in vitro growth conditions. BRMS1 expression significantly increased multiple major histocompatability complex (MHC) genes and significantly decreased expression of several genes associated with protein localization and secretion. The pattern of gene expression associated with BRMS1 expression suggests that metastasis suppression may be mediated by enhanced immune recognition, altered transport, and/or secretion of metastasis-associated proteins. © 2007 Springer Science + Business Media B.V.