Abstract P6-07-21: High reduction of circulating tumour cells in HER2-negative locally advanced or metastatic breast cancer (LAMBC) patients treated with eribulin as third line chemotherapy (ONSITE study)
Authors: Manso Sánchez L , Moreno Antón F , Izarzugaza Perón Y , Delgado Mingorance I , Borrega García P , Echarri González MJ , Martínez Jáñez N , López González A , Olier Garate C , Ballesteros García A , Chacón López-Muñiz I , Ciruelos Gil EM , García Sáenz JA , Paz-Ares Rodríguez L 
Published: March 2017

Abstract
Background Circulating tumour cells (CTC) may be a good biomarker to guide the management of patients with LAMBC (Cristofanilli, NEJM 2004). Detection of CTCs in peripheral blood is a simple procedure. Eribulin monotherapy has shown improved survival in patients with LAMBC that has progressed after 2 or 3 chemotherapy regimens (EMBRACE study). The aims of this study were to evaluate the kinetics of CTCs before and after eribulin treatment, and its correlation with clinical outcomes.
Methods Patients received eribulin (1.23 mg/m2 on days 1 and 8 of every 21-day cycle) as third-line therapy until progression, unacceptable toxicity or withdrawal. CTCs were measured in 7.5ml of blood at baseline and after the second cycle of treatment. Cell counting was performed using the CellSearch System, Veridex. Cox proportional hazards regression modeling was used to identify independent prognostic factors for survival endpoints.
Results Out of 59 eligible women (mean age 57.7 years), 58 (98.3%) had received previous taxanes and/or anthracyclines. Nearly all (98.3%) had HER2-negative tumors, 72% were positive for estrogens, 21% were triple-negative; 64.4% had liver metastasis and 57.6% bone metastasis. The mean number of administered cycles was 6.9 ± 5.4. Follow-up was performed in 54 patients, with 18.5% (n=10) partial response, 42.6% (n=23) stable disease, and 38.9% (n=21) progressive disease. Clinical benefit was achieved in 33 patients (61.1%). Median progression-free survival (PFS) was 5.13 months (95% CI 3.23, 8.90) and median overall survival (OS) was 13.6 months (95% CI 11.8, not reached). CTC levels were measured in 50 patients. The mean number of CTCs at baseline was 16.8 (IQR 0-21) and on cycle 2, 5.4 (IQR 0-8.5), p&lt;0.001. In patients with CTC ≥ 5 at baseline, 52.4% reduced their levels to CTC &lt; 5 on cycle 2 (p=0.043). No significant differences (p=0.066) were found in PFS when baseline CTC levels were &lt; 5 or ≥ 5 cells/ml. Statistical differences were, however, found in OS (p= 0.0083). On cycle 2, significant differences were observed for both PFS (p=0.045) and OS (p=0.0129) with CTC levels &lt;5 or ≥ 5 cells/ml. No correlation could be found between CTC levels and the objective response at baseline or on cycle 2.
Conclusions Our study suggests there is a significant correlation between levels of CTCs and disease prognosis. Eribulin monotherapy was related to a significant reduction in CTCs.
(EudraCT number 2013-001416-30).
Keywords eribulin, metastatic, breast cancer, circulating tumour cells.
Citation Format: Manso Sánchez L, Moreno Antón F, Izarzugaza Perón Y, Delgado Mingorance I, Borrega García P, Echarri González MJ, Martínez Jáñez N, López González A, Olier Garate C, Ballesteros García A, Chacón López-Muñiz I, Ciruelos Gil EM, García Sáenz JA, Paz-Ares Rodríguez L. High reduction of circulating tumour cells in HER2-negative locally advanced or metastatic breast cancer (LAMBC) patients treated with eribulin as third line chemotherapy (ONSITE study) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-07-21.