Background: Circulating tumor cells (CTCs) are detected in peripheral blood of breast cancer patients, and they may play an important role as a prognostic and predictive marker. We conducted this study to determine the presence of CTCs with the CellSearch System™ and the clinical significance in treatment of metastatic breast cancer (MBC).
Method: Twenty-eight MBC patients were enrolled. These patients were followed by assessing CTCs, imaging studies, and serum tumor markers. Blood samples were collected before starting a new treatment and at the treatment evaluation period (2-3 months after starting chemotherapy). The cutoff for CTC level was 5.
Results: At baseline, 9 of 28 patients (32%) had ≥5 CTCs per 7.5 mL of blood. At the evaluation period, 5 of 23 patients (22%) had ≥5 CTCs. The baseline CTC number did not contribute to determine their overall survival (OS); however, CTCs at the evaluation period were available to predict their OS (p < 0.001). In two cases, both CTCs and tumor markers were available as predictors of treatment efficacy. In two other cases, although alterations of tumor markers might not reflect disease condition, CTC alteration corresponded to their condition. One patient who had multiple skeletal metastasis only, experienced a decrease in her CTCs in spite of tumor marker alteration.
Conclusions: We suggest that monitoring the number of CTCs may be helpful in predicting the efficacy of the treatment and the prognosis. CTCs might be especially useful with patients whose lesions are difficult to assess.