Flow cytometric detection of circulating endothelial cells and endothelial progenitor cells in healthy subjects

Clinical Efficacy of the HIV Protease Inhibitor Indinavir in Combination with Chemotherapy for Advanced Classic Kaposi Sarcoma Treatment: A Single-Arm, Phase II Trial in the Elderly

Kaposi sarcoma is a rare angioproliferative disease associated with human herpes virus-8 (HHV-8) infection. Kaposi sarcoma is frequent and aggressive in HIV-infected people, whereas the classic form (CKS) generally has an indolent course. Notably, all conventional therapies against Kaposi sarcoma have only temporary efficacy. We have previously shown that indinavir, a HIV protease-inhibitor with direct antiangiogenic and antitumor activity, is safe and effective in patients with early CKS, whereas effects are less prominent in advanced disease, probably due to the larger tumor mass. Therefore, the clinical response to indinavir was assessed in patients with advanced CKS after debulking chemotherapy. This was a monocentric phase 2 trial in elderly with progressive/advanced CKS treated with debulking chemotherapy and indinavir combined, followed by a maintenance phase with indinavir alone. Secondary endpoints included safety and Kaposi sarcoma biomarker evaluation.All evaluable patients (22) responded to debulking therapy. Out of these, 16 entered the indinavir maintenance phase. The overall response rate at end of maintenance was 75% (estimated median response-duration 43 months). Moreover, most responders showed further clinical improvements (lesion number/nodularity) during maintenance and post-treatment follow-up. Notably, after relapse, progressors did not require systemic Kaposi sarcoma therapy and showed clinical improvements (including disease stabilization) remaining on study. Responders also showed immune status amelioration with a consistent B-cell increase and positive changes of other biomarkers, including anti-HHV-8 natural killer activity. In advanced CKS a strategy combining indinavir and chemotherapy is safe and associated with high and durable response rates and it could be rapidly adopted for the clinical management of these patients.

SIGNIFICANCE

This phase-2 trial showed that the HIV protease inhibitor indinavir may boost and extend the duration of the effects of chemotherapy in elderly with advanced progressive classic Kaposi sarcoma, without additional toxicity. Further, the amelioration of the immune status seen in responders suggests a better control of HHV-8 infection and tumor-cell killing. Thus, indinavir combined with chemotherapy may represent an important tool for the clinical management of classic Kaposi sarcoma in elderly patients.

A phase I study of docetaxel plus synthetic lycopene in metastatic prostate cancer patients

PURPOSE

Our preclinical studies showed that lycopene enhanced the anti-prostate cancer efficacy of docetaxel in animal models. A phase I trial (NCT0149519) was conducted to identify an optimum dose of synthetic lycopene in combination with docetaxel (and androgen blockade [androgen deprivation therapy, ADT]), and to evaluate its effect on the safety and pharmacokinetics of docetaxel in men with metastatic prostate cancer.

METHODS

Subjects were treated with 21-day cycles of 75 mg/m2 docetaxel (and ADT), plus lycopene at 30, 90 or 150 mg/day. A Bayesian model averaging continual reassessment method was used to guide dose escalation. Pharmacokinetics of docetaxel and multiple correlative studies were carried out.

RESULTS

Twenty-four participants were enrolled, 18 in a dose escalation cohort to define the maximum tolerated dose (MTD), and six in a pharmacokinetic cohort. Docetaxel/ADT plus 150 mg/day synthetic lycopene resulted in dose-limiting toxicity (pulmonary embolus) in one out of 12 participants with an estimated probability of .106 and thus was chosen as the MTD. Lycopene increased the AUCinf and Cmax of plasma docetaxel by 9.5% and 15.1%, respectively. Correlative studies showed dose-related changes in circulating endothelial cells and vascular endothelial growth factor A, and reduction in insulin-like growth factor 1R phosphorylation, associated with lycopene therapy.

CONCLUSIONS

The combination of docetaxel/ADT and synthetic lycopene has low toxicity and favourable pharmacokinetics. The effects of lycopene on biomarkers provide additional support for the toxicity-dependent MTD definition.

HIGHLIGHTS

The maximum tolerated dose was identified as 150 mg/day of lycopene in combination with docetaxel/ADT for the treatment of metastatic prostate cancer patients. Small increases in plasma exposure to docetaxel were observed with lycopene co-administration. Mechanistically significant effects were seen on angiogenesis and insulin-like growth factor 1 signalling by lycopene co-administration with docetaxel/ADT.

Circulating endothelial cells in severe Plasmodium falciparum infection

Plasmodium falciparum infection is associated with diffuse vascular dys-regulation. Levels of blood circulating endothelial cells (CECs; CD146⁺CD45^-) are a marker of vascular injury. This study aimed to measure blood CECs by flow cytometery in patients with acute malaria infection before and after treatment and to evaluate the prognostic value of that measurement for that disease. The subjects were allocated into: Group I: uncomplicated malaria (UM, n = 32), Group II: severe malaria (SM, n = 12), Group III: the treated UM (TUM, n = 32), Group IV: the treated SM (TSM, n = 12) and Group V: healthy controls (HC, n = 25). Before treatment, SM patients showed the highest mean number of CECs (30,658.3 ± 2658.2/5 × 10⁶ peripheral blood mononuclear cells (PBMCs)), followed by UM patients (19,481.56 ± 866.83/5x10⁶PBMCs) and both groups were significantly higher than HC (2034 ± 300.59/5x10⁶PBMCs, P < .001). The level of CECs decreased significantly in both infected groups after treatment; in TUM it became 5602.18 ± 509.72/5 × 10⁶PBMCs and in TSM it reached 8457.5 ± 452.4/5 × 10⁶ PBMCs (both values P < .001 in comparison with SM). By receiver operating characteristic curve analysis, the best cut-off count for CECs which enables prediction of the occurrence of severe malaria infection was 27,150/5 × 10⁶ PBMCs or more, with 100% sensitivity, 100% specificity, and 100% accuracy. CECs had a significant positive correlation with parasitemia index and serum creatinine and a significant negative correlation with hemoglobin concentration in patients with acute malaria. In conclusion, the level of CECs could be used as a biomarker denoting endothelium damage during acute P. falciparum infection, and it correlated with infection severity and predicted its prognosis.

Circulating endothelial cells and their subsets: novel biomarkers for cancer

Angiogenesis contributes to the growth of solid tumors. Antiangiogenic agents are widely used in various cancers and considerable efforts have been made in the development of novel biomarkers that can predict the outcome of an anticancer treatment. Of those, circulating endothelial cells (CECs) and their subsets constitute a surrogate tool for monitoring disease activity. However, owing to the lack of standardization on the phenotypes and detection of CECs and their subsets, results have always been inconsistent and uninterpretable. In this review, we focus on the biological characteristics in terms of physiology, phenotypes and detection of CECs along with their subsets; review the current scenario of CEC enumeration as a surrogate biomarker in clinical oncology; and explore their future potential applications.

Adipose-derived stem cell differentiation as a basic tool for vascularized adipose tissue engineering

The development of in vitro adipose tissue constructs is highly desired to cope with the increased demand for substitutes to replace damaged soft tissue after high graded burns, deformities or tumor removal. To achieve clinically relevant dimensions, vascularization of soft tissue constructs becomes inevitable but still poses a challenge. Adipose-derived stem cells (ASCs) represent a promising cell source for the setup of vascularized fatty tissue constructs as they can be differentiated into adipocytes and endothelial cells in vitro and are thereby available in sufficiently high cell numbers. This review summarizes the currently known characteristics of ASCs and achievements in adipogenic and endothelial differentiation in vitro. Further, the interdependency of adipogenesis and angiogenesis based on the crosstalk of endothelial cells, stem cells and adipocytes is addressed at the molecular level. Finally, achievements and limitations of current co-culture conditions for the construction of vascularized adipose tissue are evaluated.

Circulating endothelial cells are increased in chronic myeloid leukemia blast crisis

We measured circulating endothelial precursor cells (EPCs), activated circulating endothelial cells (aCECs), and mature circulating endothelial cells (mCECs) using four-color multiparametric flow cytometry in the peripheral blood of 84 chronic myeloid leukemia (CML) patients and 65 healthy controls; and vascular endothelial growth factor (VEGF) by quantitative real-time PCR in 50 CML patients and 32 healthy controls. Because of an increase in mCECs, the median percentage of CECs in CML blast crisis (0.0146%) was significantly higher than in healthy subjects (0.0059%, P<0.01) and in the accelerated phase (0.0059%, P=0.01). There were no significant differences in the percentages of CECs in chronic- or active-phase patients and healthy subjects (P>0.05). In addition, VEGF gene expression was significantly higher in all phases of CML: 0.245 in blast crisis, 0.320 in the active phase, and 0.330 in chronic phase patients than it was in healthy subjects (0.145). In conclusion, CML in blast crisis had increased levels of CECs and VEGF gene expression, which may serve as markers of disease progression and may become targets for the management of CML.

Clinical significance of circulating endothelial cells in patients with severe sepsis or septic shock

BACKGROUND

Endothelial damage developing in severe sepsis or septic shock results in multiorgan dysfunction. An increased circulating endothelial cell (CEC) count represents a novel marker of endothelial damage, which has been reported in cases of severe sepsis or septic shock. The aim of this study was to evaluate the clinical significance of CECs in patients with severe sepsis or septic shock.

METHODS

CECs were evaluated and quantified by flow cytometry using plasma collected from patients with severe sepsis or septic shock who were admitted to a medical intensive care unit from February 2011 to August 2011.

RESULTS

During the study period, 77 patients were enrolled. The median CEC count was 350 cells/ml (range 0-15 984 cells/ml). There was no significant difference between cases of severe sepsis and septic shock [163 cells/ml (0-15 984 cells/ml) vs 363 cells/ml (0-7884 cells/ml), p = 0.507]. There were no correlations between the number of CECs and inflammatory markers. CEC counts were significantly increased in non-survivors compared to survivors [588.5 cells/ml (1-15 984 cells/ml) vs 292 cells/ml (0-12 882 cells/ml), p = 0.044] within 28 days. The sequential-related organ failure assessment score, CEC counts ≥ 500 cells/ml and blood lactate levels were significantly associated with 28 day mortality.

CONCLUSIONS

CEC counts were higher in non-survivors of severe sepsis or septic shock and could be used as a biomarker to predict the prognosis in these patients.

Relationships between emerging cardiovascular risk factors, z-BMI, waist circumference and body adiposity index (BAI) on adolescents

OBJECTIVE

The body adiposity index (BAI) has been recently proposed as an alternative index to body mass index (BMI) and waist circumference (WC) to evaluate adiposity in adults, with special focus on its ability to discriminate gender specificities on adiposity. Endothelial dysfunction, circulating endothelial cells (CECs), endothelin-1 and adipocytokines are all related to atherosclerosis and nowadays considered as markers of emerging cardiovascular (CV) risk. This study aimed to determine in normal weight and obese adolescents which measures of body composition (BAI and z-BMI) or distribution (WC) correlate better with emerging CV risk markers.

PATIENTS

Forty adolescents were selected according to BMI: normal weight (n = 20; 7 girls/13 boys, 14·7 ± 1·4 years, 53·4 ± 6·0 kg, z-BMI 0·6 ± 0·1) and obese ones (n = 20; 13 girls/7 boys, 14·1± 1·0 years, 86·7 ± 11·5 kg, z-BMI 2·7 ± 0·4).

MEASUREMENTS

Body fat and fat mass were measured by dual-energy X-ray absorptiometry (DXA). Non-nutritive skin microvascular reactivity was evaluated by laser Doppler flowmetry with iontophoretic release of vasoactive drugs. Activated CECs were assessed by flow cytometric analysis.

RESULTS

In adolescents, the measurement of % fat by DXA showed high correlation with BAI (ρ = 0·75, P < 0·0001), z-BMI (r = 0·84, P < 0·0001) and WC (r = 0·83, P < 0·0001). Endothelin-1 and activated CECs did not correlate with any anthropometric measures while adipocytokines expressed variable associations among them. Endothelium-dependent vasodilation showed higher correlation with BAI (r = -0·51, P < 0·0001) compared to z-BMI (r = -0·40, P < 0·001) or WC (r = -0·45, P < 0·001), specially on females.

CONCLUSIONS

BAI was associated with emerging CV risk markers in adolescents but further research is needed to evaluate its potential in clinical and epidemiological sets.

Endothelial outgrowth cells: function and performance in vascular grafts

The clinical need for vascular grafts continues to grow. Tissue engineering strategies have been employed to develop vascular grafts for patients lacking sufficient autologous vessels for grafting. Restoring a functional endothelium on the graft lumen has been shown to greatly improve the long-term patency of small-diameter grafts. However, obtaining an autologous source of endothelial cells for in vitro endothelialization is invasive and often not a viable option. Endothelial outgrowth cells (EOCs), derived from circulating progenitor cells in peripheral blood, provide an alternative cell source for engineering an autologous endothelium. This review aims at highlighting the role of EOCs in the regulation of processes that are central to vascular graft performance. To characterize EOC performance in vascular grafts, this review identifies the characteristics of EOCs, defines functional performance criteria for EOCs in vascular grafts, and summarizes the existing work in developing vascular grafts with EOCs.

Circulating blood endothelial nitric oxide synthase contributes to the regulation of systemic blood pressure and nitrite homeostasis

OBJECTIVE

Mice genetically deficient in endothelial nitric oxide synthase (eNOS(-/-)) are hypertensive with lower circulating nitrite levels, indicating the importance of constitutively produced nitric oxide (NO•) to blood pressure regulation and vascular homeostasis. Although the current paradigm holds that this bioactivity derives specifically from the expression of eNOS in endothelium, circulating blood cells also express eNOS protein. A functional red cell eNOS that modulates vascular NO• signaling has been proposed.

APPROACH AND RESULTS

To test the hypothesis that blood cells contribute to mammalian blood pressure regulation via eNOS-dependent NO• generation, we cross-transplanted wild-type and eNOS(-/-) mice, producing chimeras competent or deficient for eNOS expression in circulating blood cells. Surprisingly, we observed a significant contribution of both endothelial and circulating blood cell eNOS to blood pressure and systemic nitrite levels, the latter being a major component of the circulating NO• reservoir. These effects were abolished by the NOS inhibitor L-NG-nitroarginine methyl ester and repristinated by the NOS substrate L-arginine and were independent of platelet or leukocyte depletion. Mouse erythrocytes were also found to carry an eNOS protein and convert (14)C-arginine into (14)C-citrulline in NOS-dependent fashion.

CONCLUSIONS

These are the first studies to definitively establish a role for a blood-borne eNOS, using cross-transplant chimera models, that contributes to the regulation of blood pressure and nitrite homeostasis. This work provides evidence suggesting that erythrocyte eNOS may mediate this effect.

Comparative characteristics of endothelial-like cells derived from human adipose mesenchymal stem cells and umbilical cord blood-derived endothelial cells

Adult peripheral blood contains a limited number of endothelial progenitor cells that can be isolated for treatment of ischemic diseases. The adipose tissue became an interesting source of stem cells for regenerative medicine. This study aimed to investigate the phenotype of cells obtained by culturing adipose-derived mesenchymal stem cells (ad-MSCs) in the presence of endothelial growth supplements compared to endothelial cells obtained from umbilical cord blood (UCB). Passage 3 ad-MSCs and mononuclear layer from UCB were cultured in presence of endothelial growth media for 3 weeks followed by their characterization by flow cytometry and polymerase chain reaction. After culture in endothelial inductive media, ad-MSCs expressed endothelial genes and some endothelial marker proteins as CD31 and CD34, respectively. Adipose tissue could be a reliable source for easy obtaining, expanding and differentiating MSCs into endothelial-like cells for autologous cell-based therapy.

A systematic approach to the establishment and characterization of endothelial progenitor cells for gene therapy

It has been recently demonstrated that endothelial progenitor cells (EPCs) have increasing potential for gene therapy or regenerative cell therapy for cardiovascular diseases and cancer. However, current therapies involving EPCs are inefficient because of the very low level of EPCs in the available sources, for example, in blood. One solution is to derive in vitro an expanded population of EPCs from circulation. In addition, EPCs like other progenitor cells have an intrinsic predisposition of differentiating into mature cell types, for example, mature endothelial cells; therefore, establishing a sufficient amount of EPCs alongside maintaining the EPC characteristic phenotype during genetic modification and long-term culture presents a significant challenge to the field of gene and cell therapies. In this study, we have systematically investigated EPCs from different sources and used multiple parameters, including cell surface markers and a tubule formation assay to identify factors that influence the establishment, characteristics, and vector transduction capability of EPCs. Our results show the considerable promise, as well as certain limitations in the establishment and manipulation of genetically modified EPCs for gene therapy. While obtaining high transduction efficiency and robust in vitro tubule formation of EPCs using lentiviral vectors, we also observed that lentiviral vector transduction significantly altered EPC phenotype as demonstrated by an increased percentage of CD34(+) progenitor cells and increased expression of adhesion molecule CD144 (VE-cadherin). Taking account of the increased expression of CD144 reported in cancer patients, the altered expression of EPC-related markers, for example, VE-cadherin and the enrichment of CD34(+) cells, after vector transduction indicates the importance of extensive characterization and vigorous safety control of genetically modified EPCs before they are accepted for clinical use.

Molecular markers to predict outcome to antiangiogenic therapies in colorectal cancer: current evidence and future perspectives

Angiogenesis is a universal requirement for the growth of solid tumours beyond the limits of oxygen diffusion from the existing vasculature. The expression and function of proangiogenic and antiangiogenic factors are altered in solid malignancies to drive net neoangiogenesis. Vascular endothelial growth factor (VEGF) has been confirmed in several clinical trials as an important therapeutic target in colorectal cancer (CRC) treatment. However, given that the efficacy of antiangiogenic agents appears to be limited to a subset of patients, the identification of who will obtain the greater benefit from this therapy or suffer from specific toxicities and when or for how long they should be administered in the treatment algorithm are major open questions for clinicians and challenges for present and future research. Current evidence indicates some predictive value for particular circulating measures, such as an increase in VEGF, a decrease in vascular endothelial growth factor receptor 2 (VEGFR-2) or circulating endothelial cells, tissue biomarkers, microvessel density, KRAS and BRAF gene mutations or polymorphisms affecting components of the VEGF pathway. Many questions relating to these and other surrogate biomarkers, however, remain unanswered and their clinical usefulness has yet to be proven. This review will focus on the present status of knowledge and future perspectives for developing molecular tools to foresee and monitor antiangiogenic therapy activity in CRC patients.

Biochemical markers of aging for longitudinal studies in humans

Much progress has been made in the past decades in unraveling the mechanisms that are responsible for aging. The discovery that particular gene mutations in experimental species such as yeast, flies, and nematodes are associated with longevity has led to many important insights into pathways that regulate aging processes. However, extrapolating laboratory findings in experimental species to knowledge that is valid for the complexity of human physiology remains a major challenge. Apart from the restricted experimental possibilities, studying aging in humans is further complicated by the development of various age-related diseases. The availability of a set of biomarkers that really reflect underlying aging processes would be of much value in disentangling age-associated pathology from specific aging mechanisms. In this review, we survey the literature to identify promising biochemical markers of aging, with a particular focus on using them in longitudinal studies of aging in humans that entail repeated measurements on easily obtainable material, such as blood samples. Our search strategy was a 2-pronged approach, one focused on general mechanisms of aging and one including studies on clinical biomarkers of age-related diseases.

Enhanced anti-tumor and anti-angiogenic effects of metronomic cyclophosphamide combined with Endostar in a xenograft model of human lung cancer

Standard chemotherapy for advanced NSCLC has reached a therapeutic plateau. More effective strategies must be explored. The purpose of this study was to evaluate the role of metronomic chemotherapy combined with an angiogenesis inhibitor in non-small cell lung cancer (NSCLC). A total of 114 BALB/c nude mice were inoculated subcutaneously with human NSCLC cells (A549), and when xenograft tumors were palpable, mice were randomly injected with saline as controls (Ctrl), or treated with metronomic cyclophosphamide (MET CPA), recombinant human endostatin, Endostar (Endo), MET CPA combined with Endostar (MET CPA + Endo) or maximum tolerance dose of CPA (MTD CPA), respectively. The growth of xenograft tumors and mouse survival were monitored. The frequency of peripheral blood circulating endothelial cells (CECs), microvessel density (MVD) and pericyte coverage was determined using flow cytometry and immunofluorescence staining. In comparison with the controls, treatment with either drug significantly inhibited the growth of xenograft tumors in mice. Treatment with MET CPA or Endostar, but not with MTD CPA, significantly reduced the frequency of peripheral blood total and viable CECs and the value of MVD. Endostar also considerably reduced pericyte coverage in xenograft tumors. Moreover, MET CPA combined with Endostar further reduced the frequency of peripheral blood CECs, the value of MVD, and pericyte coverage, with concomitant delay in tumor growth and extension of mouse survival. Our results indicate that MET CPA combined with Endostar results in enhanced anti-tumor and anti-angiogenic effects in a xenograft model of human lung cancer. Combined therapy with metronomic chemotherapy and an angiogenesis inhibitor may serve as a promising treatment strategy for patients with advanced NSCLC.

Circulating endothelial cells and their apoptotic fraction are mutually independent predictive biomarkers in Bevacizumab-based treatment for advanced colorectal cancer

BACKGROUND

Bevacizumab has shown consistent clinical efficacy in metastatic colorectal cancer (mCRC), but some patients respond better than others. Thus, it is crucial to identify biomarkers that permit the recognition of potentially responsive subjects and to spare toxicity in those who are unlikely benefit from treatment.

METHODS

In 24 mCRC patients undergoing Bevacizumab-based first-line treatment, we assessed by multiparameter flow cytometry changes in circulating endothelial cell (CEC) number, their apoptotic fraction (APO-CEC) and their mutual relationship. Data were compared with those from a group of 21 healthy subjects.

RESULTS

CECs and APO-CECs were higher in patients versus controls (p = 0.01 and p > 0.05, respectively). The increase in CECs at the 3rd cycle in complete response (CR) patients was statistically significant (p = 0.048). A better progression-free survival was evidenced in patients that showed an increase in CECs at the 6th cycle (p = 0.009). Regarding the changes in CECs and APO-CECs, a strong correlation was evidenced, at baseline, both in the global population (0.002; r: 0.53) and in the CR subgroup (p: 0.02; r: 0.77). In the partial response + stable and progression disease (SD + PD) subgroup, this correlation was highly significant at the 6th cycle (p: 0.001; r: 0.83).

CONCLUSIONS

We confirmed the predictive role of an increase in CECs in mCRC patients treated with Bevacizumab-based therapy and showed that modifications in CECs and APO-CECs are independent factors. This underlines the relevance of a simultaneous quantitative and functional evaluation of these biomarkers in view of their possible diagnostic utility.

Arterial erectile dysfunction: reliability of new markers of endothelial dysfunction

OBJECTIVE

Blood endothelial progenitor cells (EPC) and microparticles (EMP) have been proposed as markers of endothelial dysfunction. Aim of this study was to evaluate a new immunophenotype of EPC and EMP in patients with arterial erectile dysfunction (AED) compared to psychogenic erectile dysfunction (PED).

MATERIALS AND METHODS

One hundred patients (63.2±2.6 yr) with AED were enrolled in this study. Their EPC and EMP concentrations were compared to those of 40 patients with PED (64.2±2.7 yr). EPC (CD45(neg)/CD34(pos)/ CD144(pos)) and EMP (CD45(neg)/CD144(pos)/AnnexinV(pos)) blood concentrations were evaluated by flow cytometry.

RESULTS

Patients with AED had significantly higher blood pressure, triglycerides, homeostasis model assessment index of insulin resistance, and cavernous artery acceleration time and intima-media thickness than PED; whereas international index of erectile function 5 score, HDL-cholesterol, and cavernous artery peak systolic velocity was lower than PED. Both EPC and EMP were significantly higher in patients with AED compared to patients with PED.

CONCLUSIONS

Patients with AED showed worse metabolic parameters, cavernous artery parameters, and higher EPC and EMP compared to patients with PED. This suggests that AED is an expression of endothelial dysfunction and that EPC and EMP may be considered predictors of endothelial dysfunction in patients with AED.

Circulating endothelial cells and endothelial progenitors as predictive markers of clinical response to bevacizumab-based first-line treatment in advanced colorectal cancer patients

BACKGROUND

Despite the consistent clinical results demonstrated by studies on anti-angiogenic drugs targeted against the vascular endothelial growth factor in metastatic colorectal cancer (mCRC) patients, no specific direct/indirect biomarker of their efficacy has been validated. In this field, circulating endothelial cells (CECs) and endothelial progenitor cells (CEPs) have recently been proposed as noninvasive biomarkers.

PATIENTS AND METHODS

The absolute numbers of CEPs, total CECs (tCECs) and their resting (rCECs) and activated subsets were evaluated by multiparameter flow cytometry in 40 mCRC patients at baseline and before the administration of the third and sixth course of a bevacizumab-based first-line treatment. Fifty healthy subjects were utilized as control.

RESULTS

The overall response rate was 80%, overall clinical benefit was 90% and median progression-free survival (PFS) was 13.8 months. In our patients, tCECs and rCECs were significantly increased compared with healthy subjects. The patients who achieved a radiological response showed, at baseline, a significant decrease of rCECs and a trend in decrease of tCECs in comparison with patients not achieving response. Finally, a baseline absolute number of tCEC and rCEC <40 cells/ml was evidenced in patients with a longer PFS. No correlation was found regarding CEP.

CONCLUSIONS

Our study suggests significant correlations between both tCEC and rCEC baseline levels and the antitumor efficacy of a bevacizumab-based combination therapy in mCRC patients, thus confirming that these biomarkers could be used in the clinical setting as an early predictor of tumor response.