Circulating tumor cells (CTCs) in patients with HER2-negative recurrent or metastatic breast cancer treated with eribulin as third-line therapy: ONSITE trial (OncoSur Analysis of the Treatment in Third Line of ABC with Eribulin).

e22042 Background: CTCs in peripheral blood are an ideal source for the detection of tumor dissemination. Their poor prognosis significance (CTCs > 5) has been demonstrated in metastasic breast carcinoma (Cristofanilli, NEJM 2004). Eribulin (E) is indicated for the treatment of patients with locally advanced or metastatic breast cancer who have progressed after at least one chemotherapeutic regimen for advanced disease. Onsite trial is a multicentre, single arm, study to evaluate the safety of Eribulin as third line of chemotherapy in advanced breast cancer (ABC) progressed to anthracycline and a taxane. Aims of this sub-study are the evaluation of the prevalence and kinetics of CTCs before and after treatment with E in pts with MBC in third line Methods: A total of 57 patients received E (1.23 mg/m2 on Days 1 and 8 of every 21-day cycle) as third-line therapy, until disease progression, unacceptable toxicity or withdrawal. CTCs were measured in 7.5ml of blood at baseline and after the first cycle of treatment and enumeration were performed by CellSearch System, Veridex LCC Results: CTCs data were available for 44 pts. The media value of CTCs at baseline determination was 17 cells (min 0- max 21) and 5 cells (min 0-max 8) in second determination, p = 0,002. Baseline value of CTCs > 5 was presented in 36% of the pts and in 22% after first cycle, p = 0,033. After 1st cycle of eribulin 84% of pts presented a CTCs value < 5. First follow-up was made in 26 pts after 3 months of treatment with CR 0%, PR 9% (n = 5), ED 21% (n = 11), PD 18% (n = 10). 55% (N = 10) of pts that had stable disease/partial response, decreased or maintained CTCs value < 5 post-treatment. Conclusions: Treatment with eribulin in third line ABC was related with a high reduction of poor prognosis value of CTCs > 5 and baseline CTCs counts. Clinical trial information: 2013-001416-30.