Metastasis suppressor 1 (MTSS1) may play an important role in cancer metastasis. Firstly, this study assessed MTSS1 expression levels within breast cancer patients to reveal any clinical relevance. Secondly, we aimed to clarify the cellular function of MTSS1 in breast cancer cells. MTSS1 expression levels were assessed in a cohort of breast cancer specimens (normal n=33; cancer n=127), through quantitative PCR analysis and immuno-histochemical techniques. The influence of MTSS1 was further examined via biological overexpression and knockdown within breast cancer cell lines. We report that patients with tumours expressing reduced levels of MTSS1 had a poorer prognosis (p=0.042). High levels of MTSS1 correlated with an increased patient overall survival (p=0.0108) and disease-free survival (p=0.012). Furthermore, overexpression of MTSS1 significantly suppressed (p<0.01) the invasive, migratory, growth and adherence properties of a human breast cancer cell line. In contrast, knockdown of MTSS1 dramatically enhanced these properties. We conclude that MTSS1 is a prognostic indicator of disease-free survival in breast cancer patients and demonstrates the ability to play a role in governing the metastatic nature of breast cancer cells.