Evidence for the use of circulating tumor cells in the prognostic stratification of women with metastatic breast cancer

In conclusion, the results of our study, in conjunction with the data already published, provide evidence of the prognostic power of CTCs among women with newly diagnosed MBC. We believe that the evidence is sufficient to propose a new stratification system for MBC whereby CTCs measured at diagnosis is used to classify stage IV disease into stage IVA (CTCs <5) and stage IVB (CTCs =5). This system would allow not only for a biological distinction of prognosis at diagnosis but would also allow for designing clinical trials specifically aimed at women with more aggressive, poor prognosis, stage IVB disease. With further research, the application of CTCs will likely broaden. There is already evidence to indicate that changing levels of CTCs may be a good marker of therapeutic efficacy.⁹ However, prospective studies to confirm the utility of CTCs as a marker of therapeutic efficacy are needed.