Breast cancer metastasis-suppressor 1 (BRMS1) is 246 amino acid protein that acts as a mediator of metastasis suppression in several types of cancer including ovarian, lung, bladder, and murine mammary. BRMS1 mRNA is expressed in various tissues, including ovary, prostate, testis, and colon, but the protein is primarily detected in term placenta. BRMS1 suppresses metastasis without inhibiting tumorigenicity by modifying several metastasis-associated phenotypes. BRMS1 may participate in transcriptional regulation by binding to the mSin3/histone deacetylase complex. The expression of BRMS1 in certain cells increases connexin Cx43 expression and reduces connexin Cx32 expression. This produces a gap junction that increases intercellular communication, similar to those found in normal breast tissue. BRMS1 is stabilized by Hsp90 and may inhibit NF-ⅹB activity.