Breast cancer metastasis is the leading cause of cancer deaths in women and is difficult to combat due to the long periods in which disseminated cells stay dormant and can be re-activated to start the relapse. Assessing the number and molecular profile of circulating tumor cells (CTCs) in breast cancer patients, especially in early breast cancer, should help in identifying the possibility of relapse in time for therapeutic intervention to prevent or delay recurrence. Molecular analysis of CTCs have a potential to define particular susceptibilities of the cells representing the current tumor burden, which may be considerably different from the cells of the primary tumor. While metastatic breast cancer is considered incurable this approach may offer more tailored therapy to the patients. In this article we inspect the routes to metastasis in breast cancer and how they can be linked to specific features of CTCs, how CTC analysis may be used in therapy, and what is the current status of the research and efforts to include CTC analysis in clinical practice.