Abstract P3-12-09: The prevalence and quantity of circulating tumor cells (CTCs) after adjuvant chemotherapy with and without anthracyclines in patients with HER2-negative early breast cancer (EBC)

Background: The use of anthracycline based chemotherapy in early breast cancer (EBC) patients has been well established. However, adverse effects like cardiotoxicity and efficacy in certain subgroups continue to be subjects of discussion. Based on data suggesting a limited benefit of anthracyclines in HER2-negative patients, the German SUCCESS C study randomly assigned patients with EBC to be treated with either anthracycline-containing or anthracycline-free chemotherapy. Since the prognostic value of CTCs in EBC has already been demonstrated in several trials, we compared the prevalence of CTCs after the completion of chemotherapy between both treatment arms. Methods: The SUCCESS C trial was a randomized, open-label, Phase III study comparing disease free survival (DFS) in patients with HER2-negative EBC. Treatments were either 3 cycles epirubicin, 5-fluorouracil and cyclophosphamide followed by 3 cycles of docetaxel (FEC–DOC), or 6 cycles of an anthracycline-free regimen with docetaxel and cyclophosphamide (DOC-C). The CTC status at chemotherapy cycle 6 was prospectively evaluated using the FDA-approved CellSearch System (Veridex, USA). Results: Data on CTC status after chemotherapy are available for 1757 patients. Overall, CTCs were found in 220 (12.5%) patients (median 1, range 1 – 18 CTCs). One CTC was detected in 123 (55.9%), two CTCs in 53 (24.1%), three to five CTCs in 37 (16.8%), and more than five CTCs in 7 (3.2%) of these patients. Univariate analyses revealed that CTC prevalence was not significantly associated with tumor size (pT1, pT2, pT3, pT4), nodal stage (pN0, pN1, pN2, pN3), grading (G1, G2, G3), histological type (invasive ductal, invasive lobular, other), estrogen-receptor status, or progesterone-receptor status (Chi-square tests, all p > 0.1). There was no significant difference with respect to the prevalence of CTCs after chemotherapy between the two treatment arms (Chi-square test, p = 0.23), as CTCs were detected in 11.6% (103 out of 889) of patients treated with the anthracycline-containing chemotherapy regimen and in 13.5% (117 out of 868) of patients treated with the anthracycline-free chemotherapy regimen. In addition, there was no significant difference between the two treatment arms with regard to the number of CTCs detected after chemotherapy in CTC-positive patients (FEC-DOC: median = 1, range 1 – 18; DOC-C: median = 1, range 1 – 8; Mann-Whitney U test, p = 0.30). Conclusions: The comparable prevalence and number of CTCs after the completion of chemotherapy may indicate that anthracycline-free chemotherapy is not inferior to anthracycline-containing chemotherapy in this study. This however, has to be confirmed by survival analyses, which will be available in 2014. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-12-09.