Increases in the number of circulating endothelial cells (CECs) and progenitors (CEPs) have been reported in various pathological conditions including cancer. Preclinical studies have shown that CEC and CEP kinetics correlate well with several standard laboratory angiogenesis assays, which cannot be used in humans. At the clinical level, evidence is emerging that CEC kinetics and viability might correlate with clinical outcomes in cancer patients who undergo anti-angiogenic treatment. Therefore, CEC and CEP measurement has potential as a surrogate marker for monitoring anti-angiogenic treatment and drug activity, and could help to determine the optimal biological dose of anti-angiogenic drugs, which are being used with increasing frequency in medical oncology.

SUMMARY Several hypotheses have been proposed to explain how antiangiogenic drugs enhance the treatment efficacy of cytotoxic chemotherapy including impairing the ability of chemotherapy-responsive tumors to regrow after therapy. With respect to the latter, we show that certain chemotherapy drugs, e.g. paclitaxel, can rapidly induce pro-angiogenic bone marrow derived circulating endothelial cell (CEP) mobilization, and subsequent tumor homing, whereas others, e.g. gemcitabine, did not. Acute CEP mobilization was mediated, at least in part, by systemic induction of SDF-1α and could be prevented by various procedures such as treatment with anti-VEGFR2 blocking antibodies or by paclitaxel treatment in CEP-deficient Id-mutant mice, both of which resulted in enhanced anti-tumor effects mediated by paclitaxel, but not gemcitabine.

No abstract

Treatment with metronomic capecitabine and cyclophosphamide in combination with bevacizumab was effective in advanced breast cancer and was minimally toxic. The number of baseline CECs significantly correlated with response and outcome, therefore supporting further studies on this surrogate marker for the selection of patients to be candidates for antiangiogenic treatments.