Circulating tumor cells (CTC) are an independent prognostic factor in metastatic breast cancer patients (MBC). However, CTC are undetectable in one third of patients. The aim of this study was to assess the prognostic factors in MBC patients without detectable CTC. This retrospective study included 292 MBC patients evaluated between January 2004 and December 2007. CTC were enumerated before patients started a new line of treatment using the CellSearch TM . Overall survival (OS) was calculated from the date of CTC measurement and estimated by the Kaplan-Meier product limit method. CTC were not detected in 35.96% patients, whereas 40.75% patients had CTC 5. Undetectable CTC status was positively correlated with presence of brain metastasis (OR: 6.17, 95%CI 5 2.14-17.79; p 5 0.001), and inversely correlated with bone metastasis (OR: 0.47; 95%CI 5 0.27-0.80; p 5 0.01). In multivariate analysis, hormone receptors, number of metastatic sites and lines of therapy were independent prognostic factors for OS in patients without detectable CTC. Patients without detectable CTC before starting of a new line of therapy comprise a heterogeneous group with substantially different prognosis. We showed that some important metastatic disease characteristics are predictive of undetectable CTC status in MBC.Breast cancer is one of the most common malignancies in women with estimated 182,460 new cases diagnosed in 2008.1 Despite advances in prevention, detection and adjuvant therapy of breast cancer, substantial proportions of patients are diagnosed or further develop metastatic disease. Metastatic breast cancer (MBC) patients represent a heterogeneous group whose prognosis depends on different tumor and host related factors such as tumor hormone receptor status, HER-2 status, and tumor grade, extent of disease, age, performance status and previous therapy.
2-5Circulating tumor cells (CTC) are cancer cells of epithelial origin, whose detection using the CellSearch TM system (Veridex Corporation, Warren, NJ, USA) before and during treatment represents an independent predictor of progression-free survival (PFS) and overall survival (OS) in patients with MBC. 6,7 Superior survival among patients with CTC < 5 was observed regardless of histology, hormone receptor and HER-2/neu status, sites of first metastases, or whether the patient had recurrent or de novo metastatic disease. 6,8 The prognostic value of CTC was demonstrated to be superior to tumor burden as measured by Swenertone score (quantitative scoring system to estimate the total burden of metastatic disease as the sum of the scores for tumor extent at all known disease sites) 2 or by serum tumor markers, suggesting a special biological value of CTC. The prognostic value of CTC was shown to be superior to conventional and functional imaging procedures as well. 7,9 These data suggest the possibility that CTC might represent a population of tumorigenic cancer stem cells and might play an important role in tumor dissemination. 10,11 CTC are not detectable in 30-35% of MBC patients.
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