Breast Cancer Metastasis Suppressor 1 (BRMS1) expression has been associated with longer patient survival in multiple cancer types. Understanding BRMS1 at the protein level will provide insights into both mechanism of action and enhance potential therapeutic development. We previously mapped the C terminus of BRMS1 as critical for metastasis suppression and hypothesized that critical protein interactions in this region will explain function. These studies indicate that phosphorylation status at S237 regulates BRMS1 interactions related to a variety of biological processes, phenotypes [cell cycle (e.g., CDKN2A), DNA repair (e.g., BRCA1)], and metastasis [(e.g., TCF2 and POLE2)]. Presence of the C-terminal site appears to be critical for BRMS1 directed metastasis suppression, as demonstrated by in vitro migration assays. These assays demonstrated that presence of S237 directly decreased MDA-MB-231 migration. This study furthers our understanding of the molecular role of BRMS1, as it demonstrates that the BRMS1 C-terminus is involved in direct protein-protein interactions. Several of the interacting proteins are associated with cancer and metastasis, which may result in metastasis suppression as suggested by in vitro findings.