A determination of circulating tumor cell (CTC) effectiveness for prediction of progression-free survival(PFS) and overall survival (OS) was conducted as an adjunct to standard treatment of care in breast cancermanagement. Between November 2008 and March 2009, 22 metastatic and 12 early stage breast carcinomapatients, admitted to Ankara Oncology Training and Research Hospital, were included in this prospective trial.Patients’ characteristics, treatment schedules and survival data were evaluated. CTC was detected twice byCellSearch method before and 9-12 weeks after the initiation of chemotherapy. A cut-off value equal or greaterthan 5 cells per 7.5 ml blood sample was considered positive. All patients were female. Median ages were 48.0(range: 29-65) and 52.5 (range: 35-66) in early stage and metastatic subgroups, respectively. CTC was positivein 3 (13.6%) patients before chemotherapy and 6 (27.3%) patients during chemotherapy in the metastaticsubgroup whereas positive in only one patient in the early stage subgroup before and during chemotherapy.The median follow-up was 22.0 (range: 21-23) and 19.0 (range: 5-23) months in the early stage and metastaticgroups, respectively. In the metastatic group, both median PFS and OS were significantly shorter in any timeCTC positive patients compared to CTC negative patients (PFS: 4.0 vs 14.0 months, Log-Rank p=0.013; andOS: 8.0 months vs. 20.5 months, Log-Rank p<0.001). OS was affected from multiple visceral metastatic sites(p=0.055) and higher grade (p=0.044) besides CTC positivity (log rank p<0.001). Radiological response ofchemotherapy was also correlated with better survival (p<0.001). As a result, CTC positivity was confirmed asa prospective marker even in a small patient population, in this single center study. Measurement of CTC byCellSearch method in metastatic breast carcinoma cases may allow indications of early risk of relapse or deathwith even as few as two measurements during a chemotherapy program, but this finding should be confirmedwith prospective trials in larger study populations.