Background: Recent studies revealed that temporal changes in circulating tumor cells (CTC) prevalence assessed before and immediately after adjuvant chemotherapy (CT) might indicate treatment response in early breast cancer (EBC). However, there is limited knowledge on CTC status one or more years after chemotherapy treatment. Here we present descriptive data on CTC status prospectively evaluated 2 and 5 years after primary diagnosis in the German SUCCESS A study. Methods: The SUCCESS A trial is a large, randomized, open-label, 2x2 factorial design Phase III study comparing disease free survival (DFS) in patients with EBC treated with 3 cycles of Epirubicin-Fluorouracil-Cyclophosphamide (FEC) followed by either 3 cycles of Docetaxel (D) or 3 cycles of Gemcitabine-Docetaxel (DG), and comparing DFS in patients treated with 2 years or 5 years of Zoledronate. CTC status at various time points was assessed using the FDA-approved CellSearch System (Veridex, USA). Results: Data on CTC status both at 2 years and at 5 years after primary diagnosis were available for 983 (26.2%) out of 3754 randomized patients. After 2 and 5 years, CTCs were found in 132 (13.4%; median 1; range 1 – 99) and 88 (9.0%; median 1; range 1 – 60) patients, respectively. The majority of patients (n = 779; 79.2%) had no CTCs at any of the two time points. CTCs were found at 2 years but not at 5 years after primary diagnosis in 116 (11.8%) patients, at 5 years but not at 2 years of follow-up in 72 (7.3%) patients, and both at 2 and at 5 years of follow-up in 16 (1.6%) patients. Conclusions: CTCs in peripheral blood were detected in a subset of early breast cancer patients without relapse up to five years after primary diagnosis. These CTCs may indicate the presence of occult “dormant” micrometastases.