Circulating tumor cells as an early predictive marker of disease progression in metastatic breast cancer patients

Circulating tumor cells (CTCs) are a prognostic marker in metastatic breast cancer, but their predictive value to monitor treatment efficacy still needs further investigation. The aim of this study was to test whether persistent elevation of circulating tumor cells (CTCs) at both baseline and before 2nd cycle of a new treatment can serve as an early predictive marker of disease progression in patients with metastatic breast cancer using the predefined 5 CTC/7.5 ml threshold. Eighty-five patients with stage IV breast cancer who met the eligibility criteria were enrolled in the study. Before starting a new treatment, all patients underwent full imaging studies and blood sampling for CTC enumeration. Patients with < 5 CTC/7.5 ml blood detected at baseline had no further CTC count. Patients with ≥ 5 CTCs /7.5 ml blood had another blood sampling for estimation of CTC before the 2nd cycle (C2). Radiological assessment of disease status was done every 9 to 12 weeks. Disease response was assessed according to the Response Evaluation Criteria In Solid Tumors (RECIST). At baseline, 44 (51.8%) of the 85 eligible patients did not have increased CTC levels. Of the other 41 patients with ≥ 5 CTCs /7.5 ml blood, only 38 patients had CTCs evaluation at first follow-up before 2nd cycle (CTCFU) that showed 25 (65.8 %) patients had < 5 CTC/7.5 ml blood and 13 (34.2%) patients had ≥ 5 CTCs /7.5 ml blood. Seventy-five patients (75/85, 88.2 %) underwent radiological restaging. According to RECIST, 36 (48%) patients were scored as having a partial response, 19 (25.3%) as having stable disease, and 20 (26.7%) as having progressive disease. Radiologic response was concordant with follow-up CTC levels in 76.5% of cases. Survival of our patients depended significantly on both the results of CTC evaluation and radiological response. The median follow-up was 18.0 [1–60] months. This study supports the significance of elevated CTCs before C2 in MBC patients starting a new line of chemotherapy as an early predictive marker of disease progression, thus, monitoring treatment benefit. It confirmed the independent prognostic significance of CTCs.