Change in circulating endothelial cells (CEC) predicts progression free survival (PFS) in patients (pts) with hormone receptor positive metastatic breast cancer (MBC) receiving letrozole (L) and bevacizumab (B)

Abstract

3039 Background: Antiangiogenic therapy has demonstrated efficacy in the treatment (tx) of metastatic breast cancer. Mechanism-based biomarkers of antiangiogenic therapy, if clinically validated, offer the potential to optimize this novel therapy. CECs have been proposed as a marker of tumor progression and/or response to antiangiogenic therapy with B. We performed a feasibility study testing B combined with L for the tx of hormone receptor-positive MBC. To explore markers of activity and response, we assayed CECs and circulating tumor cells (CTCs) at weeks (wks) 0 (baseline), 3, 12, and then Q 12 wks. Methods: CECs were defined as CD34/31+, CD45-. Progenitor (CD133+) (CECp) and activation markers (CD106+) were also measured. For CECs, 50 ul of blood was stained with the indicated MAbs; after RBC lysis, flow cytometry (FC) was performed for total CEC and CECp. For CTCs, 20 ml of blood was subjected to immunomagnetic capture using anti-EpCAM ferrofluid, followed by FC for EpCAM, CD45, and nucleic acid content. The log rank test was used to test for significant differences related to response. Results: 32 of 42 pts have been enrolled. As separately reported, prior non-steroidal AI (NSAI) use without progression is permitted; median (med) time on L before start of B was 6 mo (1–52). 28 pts have at least baseline and week 3 CEC and CTC along with clinical response data. Med CEC level at baseline was 10.4 CEC/ul (4–38); the peak value at any time point was 107. CTC levels were much less frequent with a med of 0.3 CTC/ml (0–95, and highest value 1153). An increase in CECs at wk 3 compared to wk 0 predicted worse PFS (p = 0.015). CTCs were ≤ 0.1 at study start in 40% of pts and ≥ 1.0 in only 17%, likely due to length of prior L; change in values at wk 3 did not correlate with PFS in this pretreated group. Conclusions: Consistent with our previous results in a separate trial of B containing treatment in MBC, changes in CEC levels appear to be a biomarker of response/progression on antiangiogenic therapy. CTCs did not reflect response or progression in this population of patients, likely due to lengthy prior exposure to letrozole. Supported in part by Genentech and Novartis. [Table: see text]

Defining human endothelial progenitor cells

“…reported that CEC can be defined as a discrete population of cells expressing CD31 bright CD45 − CD34 dim CD133 − whereas CPC can be defined as CD31 + CD45 dim CD34 bright CD133 + cells. Use of this protocol permitted identification of CEC at a frequency of 0.1%–6.0% of blood mononuclear cells and has been used as a marker for the predicting the outcome of women with breast cancer [30].…”

In Reply

“…In fact, by using a published flow cytometry protocol, 6 we and others discovered the existence of several subpopulations of mononuclear cells that display an endothelial phenotype in blood of rectal cancer patients. 1,[7][8][9] This finding was confirmed now in blood analyses in patients suffering of ovarian cancer, glioblastoma, sarcoma, or pediatric tumors 10 (and un-published results). The two populations that we studied in depth as biomarkers of antiangiogenic treatment were CD31 bright CD34 dim CD133 -CD45cells (referred to as viable CECs in our reports) and CD31 ϩ CD133 ϩ CD34 bright CD45 dim circulating progenitor cells (See Figs 1A and 1B and supplemental Fig 1 in our article 1 ).…”

“…The two populations that we studied in depth as biomarkers of antiangiogenic treatment were CD31 bright CD34 dim CD133 -CD45cells (referred to as viable CECs in our reports) and CD31 ϩ CD133 ϩ CD34 bright CD45 dim circulating progenitor cells (See Figs 1A and 1B and supplemental Fig 1 in our article 1 ). Our reasons for focusing on these two populations were threefold: these cells have a typical endothelial and progenitor phenotype, respectively, and thus, their blood concentration may be affected by antiangiogenic therapy; these cells were consistently detected in numbers that allowed kinetic analyses by flow at different time points during treatment with antiangiogenic agents in several hundred patient samples (after acquiring 50,000 to 150,000 gated cellular events and excluding red cells and fragments from each sample); and we and others have discovered promising clinical correlations between the concentration of these two populations and the effect of antiangiogenic therapy and/or tumor response in phase I-II clinical trials of antiangiogenic therapy [7][8][9]11 (and unpublished results). These viable CEC/progenitors were CD34 ϩ cells identified by gating on mononuclear events, which makes it highly unlikely to be contaminated by platelets.…”

Femara® and the future: tailoring treatment and combination therapies with Femara

“…Median progression-free survival was reported to be 10 months, and this compares favorably with the published data on median time to progression with first-line letrozole (9.4 months) [ 70 ]. However, analysis of efficacy and biomarker data was confounded by the long duration of prestudy aromatase inhibition [ 54 , 71 ]. Nevertheless, when the data were corrected for duration of previous AI therapy, the study did determine that changes in circulating endothelial cell (CEC) levels may be a biomarker of response or progression on anti-angiogenic therapy [ 71 ].…”

“…However, analysis of efficacy and biomarker data was confounded by the long duration of prestudy aromatase inhibition [ 54 , 71 ]. Nevertheless, when the data were corrected for duration of previous AI therapy, the study did determine that changes in circulating endothelial cell (CEC) levels may be a biomarker of response or progression on anti-angiogenic therapy [ 71 ]. Based on these findings, a randomized, double-blind, placebo-controlled trial of bevacizumab combined with endocrine therapy in patients with ER+ or PR+ metastatic breast cancer has been initiated by the Cancer and Leukemia Group B (CALGB) (see Fig.…”