Abstract 4720: Incremental increase in VEGFR1+ and VEGFR2+ hemangiogenic progenitor cells predict relapse and tumor response in breast cancer (BC) patients

Background: BC can relapse years after initial diagnosis. In animal models, bone marrow (BM)-derived VEGFR1+ cells define the premetatastic niche and VEGFR2+ cells are critical for the transition from micro- to macrometastatic disease. We sought to define the temporal relationship of these circulating hemangiogenic progenitor cells in a cohort of BC patients (pts) that developed recurrent disease and whether quantitative changes in these cells could predict response to therapy in pts with established metastases. Methods: 125 pts with Stages I to IV BC enrolled in 2 studies. In Study #1 circulating VEGFR1+ (CD45+/CD34+/VEGFR1+) hematopoietic progenitor cells (HPCs) and VEGFR2+ (CD45dim/CD133+/ VEGFR2+) endothelial progenitor cells (EPCs) of adjuvant patients were assessed at baseline (BL), every 3 months (mo) for the first year, then every 6 mo. Stage IV pts had levels measured at BL (defined as when initiating new treatment (tx)), with subsequent 1 mo interval blood draws and accompanied by a clinical evaluation. Tx could include chemo-, hormone or biologic therapy. In Study #2, these cells were examined monthly in pts without overt evidence of BC. HPCs/EPCs were quantified from peripheral blood mononuclear cells using flow cytometry with commercially available antibodies. Statistical analysis is by Wilcoxon signed-rank test. Results: Data from both studies were combined to analyze 1) pts without overt BC who relapse and 2) stage IV pts according to response. Seven pts without evidence of BC based on physical exam, labs, and imaging developed recurrence while on study. In all 7 pts, there was a median (med) increase of 1,111% in HPCs preceding overt relapse (range 283% to 5800%). Med HPCs at BL 0.65/ul (range 0.02 to 1.22/ul) increased to 2.90/ul prior to relapse (range 1.18 to 34.94/ul), p=0.016. In 5 of 7 relapsed pts a 433% increase in EPCs occurred as HPCs decreased: med EPCs at BL 0.03/ul (range 0.015 to 0.21/ul) and at relapse 0.16/ul (range 0.03 to 0.27/ul). This pattern was not seen in non-relapsed pts. In 22 stage IV pts, HPCs and EPCs were evaluated over the course of 40 tx. For the 20 tx (16 pts) in which progression of disease (POD) was the outcome, HPCs increased prior to POD (median 7.45/ul, range 0.37 to 77.6/ul) from BL (med 1.70/ul, range 0.01 to 16.47/ul), p=0.001. Similarly, EPCs increased at relapse (med 0.07/ul, range 0 to 0.62/ul) from BL (med 0.03/ul, range 0 to 0.21/ul), p=0.04. For the 12 tx (11 pts) with disease responding to syst