Objective:Triple-negative breast cancer (TNBC) is a heterogeneous disease with poor prognosis.Circulating tumor cells (CTCs) are a promising predictor for breast cancer prognoses but their reliability regarding progression-free survival (PFS) is controversial.We aim to verify their predictive value in TNBC.Methods:In present prospective cohort study,we used the Pep@MNPs method to enumerate CTCs in baseline blood samples from 75 patients with TNBC (taken at inclusion in this study) and analyzed correlations between CTC numbers and outcomes and other clinical parameters.Results:Median PFS was 6.0 (range:1.0-25.0) months for the entire cohort,in whom we found no correlations between baseline CTC status and initial tumor stage (P=0.167),tumor grade (P=0.783) or histological type (P=0.084).However,among those getting first-line treatment,baseline CTC status was positively correlated with ratio of peripheral natural killer (NK) cells (P=0.032),presence of lung metastasis (P=0.034) and number of visceral metastatic site (P=0.037).Baseline CTC status was predictive for PFS in first-line TNBC (P=0.033),but not for the cohort as a whole (P=0.118).This prognostic limitation of CTC could be ameliorated by combining CTC and NK cell enumeration (P=0.049).Conclusions:Baseline CTC status was predictive of lung metastasis,peripheral NK cell ratio and PFS in TNBC patients undergoing first-line treatment.We have developed a combined CTC-NK enumeration strategy that allows us to predict PFS in TNBC without any preconditions.