The presence of persisting CTCs after chemotherapy showed a negative influence on DFS ( HR = 1.12 ; 95 % CI = 1.02 to 1.25 ; P = .02 ) and on OS ( HR = 1.16 ; 95 % CI = 0.99 to 1.37 ; P = .06 ) CONCLUSIONS : These results suggest the independent prognostic relevance of CTCs both before and after adjuvant chemotherapy in a large prospective trial of patients with primary breast cancer .