Changes in circulating endothelial cells (CEL) in patients receiving trastuzumab for metastatic breast cancer predict response to treatment
579 Background: Amplification or overexpression of HER-2/neu has been identified in 10–20% of invasive breast cancers and is associated with shorter overall survival times; furthermore HER-2/neu is a predictive factor with regard to monoclonal antibody therapy with Trastuzumab. The observed association between the overexpression of HER-2/neu and higher VEGF expression indicates that HER-2/neu is involved, at least partly, in the regulation of angiogenesis in human breast cancer. Recently circulating endothelial cells (CECs) have been proposed as a marker of tumor progression and/or a response to antiangiogenic therapy; thus, we have performed a phase II study to explore the correlation between CECs and treatment with Trastuzumab in metastatic breast cancer Methods: 22 women aged ≥ 18 years with histologically proven Her-2-positive, ECOG performance status 0 to 2 who were not eligible for, or who wished to delay receiving chemotherapy received a standard loading dose of Trastuzumab 4 mg/Kg followed by 2 mg/Kg weekly. The weekly maintenance dose was continued until disease progression. A panel of monoclonal antibodies including anti CD45 to exclude hematopoietic cells, anti CD31, CD34, CD36, CD105, CD106, CD133, and KDR and appropriate analysis gates were used to enumerate resting and activated circulating endothelial cells Results: The overall response rate (RC + RP) to treatment was 25% (2 RC + 3RP). In healthy controls (N° 20) mean values of resting and activated CECs were 7.6/μL (4.6 - 11.2/μL) and 1.3/μL (0.1 - 2.4 /μL) respectively. Before treatment with Trastuzuamb the mean resting and activated CECs were 41.1/μL (16.4 - 60.5/μL) and 6.9/μL (5.1 - 8.7/μL). At a first assessment (6 wks) a significant decrease in CECs (p<0.001)was found in patients responding to treatment but not in the patients who did not achieve a remission Conclusions: Our finding has shown that resting and activated CECs are increased in metastatic breast cancer patients and decline during treatment in responding patients, furthermore, these data underline the crucial role of angiogenesis in this setting and support the rationale for a combination of Bevacizumab with Trastuzumab. No significant financial relationships to disclose.