Circulating Tumor Cells and Cancer Stem Cells: Clinical Implications in Nonmetastatic Breast Cancer

Despite the therapeutic advances, disease recurrence remains an ever-present threat to the health and well-being of breast cancer survivors. Assessment of circulating tumor cells (CTCs) and cancer stem cells (CSCs) during and after treatment may be of value in refining treatment.

Three 5 mL blood samples were taken from each patient: the first, at diagnosis; the second, after completion of neoadjuvant anthracyclin-based chemotherapy; and the third, a month after surgery and completion of adjuvant radiotherapy. The absolute numbers of CTCs were identified as CD45-cytokeratin+ cells. CTCs per 5 mL of blood were determined by recording all events in the whole suspension. CSCs were identified as cytokeratin⁺CD44⁺CD24-/CD45- cells. The CSCs were expressed as a percentage of CTCs.

Univariate analysis identified the measurements of baseline CTCs and CSCs, taken after chemotherapy and one month after the cessation of radiotherapy, as prognostic factors for both four-year disease-free survival and four-year overall survival. Multivariable analysis identified the third measurement of CSCs, taken one month after the completion of radiotherapy, as the only independent prognostic factor for the four-year disease-free survival (P < 0.002, hazard ratio [HR] = 1.231, 95% CI 1.077-1.407). The initial CTC measurement was the one factor that reached significance on multivariate analysis (P < 0.03, HR 1.969, 95% CI 1.092-3.551) for the four-year overall survival. Correlation was higher between CTC and CSC counts at diagnosis (r = 0.654, P < 0.001) than after chemotherapy (r = 0.317, P < 0.03), because of the more rapid decrease in the mean CTC count with chemotherapy.

The CTC count could be suitable as one of the measures for monitoring response to chemotherapy, while persistence of CSC after cessation of the treatment of nonmetastatic breast cancer, except hormonal therapy when indicated, may be a reason to consider additional therapy in the future. These findings need confirmation in larger randomized trials.