Metastatic spread of the primary tumour is responsible for the vast majority of cancer-related deaths. Detection of disseminated tumour cells in the bone marrow and circulating tumour cells in the peripheral blood is correlated with early metastatic relapse in breast cancer. Positive detection of disseminated tumour cells was associated with poor overall survival of patients. Current research has been focused on integrating minimal residual disease as a prognostic and predictive tool in the management of breast cancer. Detection of disseminated tumour cells/circulating tumour cells is not yet standardized in clinical practice because of using different enrichment and detection methods. Therefore, standardization of the used methods is necessary in the future. Previous achieved findings must be verified in larger prospective multicentre studies. Further characterization of disseminated tumour cells/circulating tumour cells will be essential for developing and monitoring the efficacy of new therapeutic concepts. The aim of this review was to provide a short survey of the metastatic cascade and cancer stem cell theory, and data on the molecular and functional characterization of disseminated tumour cells/circulating tumour cells. Finally, we discuss the potential clinical impact of disseminated tumour cells/circulating tumour cells and results of several recent studies.