Skip to main content
NCBI home page
The Oncologist logoLink to The Oncologist
. 2010 May 18;15(6):577–583. doi: 10.1634/theoncologist.2010-0029

Plasma Soluble VEGFR-1 Is a Potential Dual Biomarker of Response and Toxicity for Bevacizumab with Chemoradiation in Locally Advanced Rectal Cancer

Dan G Duda a, Christopher G Willett b,✉, Marek Ancukiewicz a, Emmanuelle di Tomaso a, Mira Shah b, Brian G Czito b, Rex Bentley c, Martin Poleski d, Gregory Y Lauwers e, Madeline Carroll b, Douglas Tyler d, Christopher Mantyh d, Paul Shellito f, Jeffrey W Clark g, Rakesh K Jain a,✉
PMCID: PMC3061828  NIHMSID: NIHMS274679  PMID: 20484123

The article explores plasma and urinary concentrations of two members of the vascular endothelial growth factor family and their receptors as potential response and toxicity biomarkers of bevacizumab with neoadjuvant chemoradiation in patients with localized rectal cancer.

Keywords: Bevacizumab, sVEGFR-1, Biomarker, Rectal cancer, Chemoradiation, Toxicity

Abstract

We explored plasma and urinary concentrations of two members of the vascular endothelial growth factor (VEGF) family and their receptors as potential response and toxicity biomarkers of bevacizumab with neoadjuvant chemoradiation in patients with localized rectal cancer. The concentrations of VEGF, placental growth factor (PlGF), soluble VEGF receptor 1 (sVEGFR-1), and sVEGFR-2 were measured in plasma and urine at baseline and during treatment. Pretreatment values and changes over time were analyzed as potential biomarkers of pathological response to treatment as well as for acute toxicity in patients with locally advanced rectal cancer treated prospectively in 2002–2008 with neoadjuvant bevacizumab, 5-fluorouracil, radiation therapy, and surgery in a phase I/II trial. Of all biomarkers, pretreatment plasma sVEGFR-1—an endogenous blocker of VEGF and PlGF, and a factor linked with “vascular normalization”—was associated with both primary tumor regression and the development of adverse events after neoadjuvant bevacizumab and chemoradiation. Based on the findings in this exploratory study, we propose that plasma sVEGFR-1 should be further studied as a potential biomarker to stratify patients in future studies of bevacizumab and/or cytotoxics in the neoadjuvant setting.

Introduction

Neoadjuvant chemotherapy and radiation therapy prior to surgery is the current standard of care for patients with advanced localized rectal carcinoma [1]. Despite the efficacy of this approach, important challenges remain in the management of patients with this malignancy. In particular, there is a critical need to improve neoadjuvant regimens and prevent or reduce metastatic dissemination. One approach may be the use of bevacizumab (Avastin®; Genentech, South San Francisco, CA), which has shown efficacy with chemotherapy in randomized phase III trials and is a current standard of care in first- and second-line metastatic colorectal cancer [2, 3]. Bevacizumab is a blocking antibody against human vascular endothelial growth factor (VEGF), a critical and highly pleiotropic factor that promotes new vessel formation in tumors [4, 5]. Bevacizumab and other anti-VEGF agents (e.g., sunitinib, sorafenib) are either approved or in late phases of development for several cancer types [6]. Several trials are under way in rectal cancer, breast cancer, and sarcoma, among others, testing the feasibility and efficacy of bevacizumab with cytotoxics as neoadjuvant treatment. In rectal cancer, several trials of bevacizumab with chemoradiation have reported promising results [7–9]. However, a major priority in clinical research in this area remains the identification of a biomarker to aid physicians in the rational selection of therapy, because not all patients benefit from these treatment approaches.

The pretreatment concentration of VEGF in tissue and in circulation has failed to predict outcome of anti-VEGF therapy in several large studies (reviewed in [10]). On the other hand, bevacizumab can increase the concentration of plasma circulating VEGF, placental growth factor (PlGF), and soluble VEGF receptor 2 (sVEGFR-2), which might represent pharmacodynamic biomarkers [9, 10]. However, it remains unknown whether these changes hold predictive biomarker value. Moreover, although the feasibility of measuring VEGF concentration in urine has been demonstrated [11], it remains unclear whether urinary biomarker changes mirror plasma biomarker changes, and whether they have potential predictive biomarker value.

Another approach might be to use a parameter or index that reflects tumor “vascular normalization.” Tumor vasculature is highly abnormal for several reasons, including local overexpression of proangiogenic factors such as VEGF or angiopoietin 2, or downregulation of endogenous antiangiogenic factors, such as thrombospondin 1 or semaphorin 3F [12–14]. Restoring the “angiogenic” balance by blocking the VEGF pathway can “normalize” the vessel structure and function, and sensitize tumors to cytotoxics [15]. Vascular normalization results in vessels that are fortified by perivascular cells and a basement membrane. Changes consistent with normalization of tumor vasculature have been demonstrated in rectal cancer patients receiving bevacizumab [9, 16, 17]. Achieving vascular normalization in tumors has been shown to be dependent on the release of another endogenous antiangiogenic factor, sVEGFR-1, by endothelial cells [18]. Circulating sVEGFR-1 can block VEGF signaling by acting as a “trap” for VEGF and proangiogenic factors from the same family, such as PlGF [19, 20]. Consistent with this function, exogenous overexpression of sVEGFR-1 inhibited tumor angiogenesis in preclinical models of cancer [21].

We recently reported the results of a phase I/II clinical trial (National Cancer Institute [NCI] #5642) incorporating neoadjuvant bevacizumab monotherapy for one 2-week cycle followed by three cycles of bevacizumab with standard 5-fluorouracil (5-FU), radiation therapy, and surgery in patients with locally advanced rectal cancer [9]. Study results have shown the feasibility of this approach, promising clinical results, and the elucidation of a critical mechanism of action of bevacizumab. In this exploratory study, we examined baseline and changes in plasma and urinary VEGF family members as potential biomarkers of response and toxicity of bevacizumab with chemoradiation in rectal cancer.

Materials and Methods

Patients

NCI #5642 was a phase I/II clinical trial of 32 patients (17 from Massachusetts General Hospital [MGH] and 15 from Duke University Medical Center) that was approved by the Cancer Therapeutics Evaluation Program of the NCI as well as the internal review boards of the Massachusetts General Hospital (2002–2008) and Duke University Medical Center (2004–2008). Informed written consent was obtained from all patients. Eligibility criteria included: histologically documented adenocarcinoma of the rectum, endorectal ultrasound or surface coil magnetic resonance imaging staged T3 or T4 primary rectal cancer, no evidence of metastatic disease, Karnofsky performance status core >70%, age >18 years, and normal hepatic, renal, and bone marrow function. All patients were treated by radiation oncologists and medical oncologists at MGH and Duke University Medical Center in collaboration with the principal investigator of this trial (Dr. Willett).

Study Treatment

Thirty-two patients received four cycles of therapy: bevacizumab infusion (5 or 10 mg/kg) on day 1 of each cycle, 5-FU infusion (225 mg/m2 per 24 hours) during cycles 2–4, external-beam radiation therapy to the pelvis (50.4 Gy in 28 fractions over 5.5 weeks), and surgery after completion of all therapy. Following recovery from surgery, 30 of 32 (94%) patients received adjuvant chemotherapy at the discretion of the treating medical oncologist. Thirteen patients received 5-FU, leucovorin, and oxaliplatin, four patients received capecitabine and oxaliplatin, 10 patients received 5-FU and leucovorin, and three patients received capecitabine. Surgical specimens were analyzed histologically to restage the rectal carcinomas and grade the regression according to Mandard criteria, and acute and postoperative adverse events were collected for all patients [9].

Measurement of Soluble Proteins From the VEGF Family in Plasma and Urine

Blood and urine samples were collected from all patients at baseline, at days 3 and 12 after bevacizumab alone, during bevacizumab with chemoradiation (day 32), and presurgery (day 96), as previously described [9]. Plasma was collected after separation using centrifugation in EDTA-coated tubes. We chose plasma for measurements because the serum concentration of sVEGFR-1, similar to VEGF, is 1.5- to twofold higher and may depend on platelet degranulation. Plasma and urine were stored in small aliquots until analyzed using standard kits from MesoScale Discovery (Gaithersburg, MD) for VEGF, PlGF, and sVEGFR-1 concentration and from R&D Systems (Minneapolis, MN) for sVEGFR-2 and creatinine concentration. (We verified in pilot studies that the range of the analytes is similar between single and multiplexed assays.)

Data and Statistical Analyses

Changes in biomarkers from baseline were expressed as ratios and tested using the exact paired Wilcoxon test. Correlations between biomarker levels and tumor regression (expressed on an ordinal scale) and between biomarker levels and the number of chemoradiation toxicities were quantified and tested using Spearman's ρ correlation coefficients. Thus, these analyses did not depend on the distributional assumptions or the choice of any biomarker threshold. Similarly, comparisons of biomarkers for binary measures of treatment response (e.g., the presence or absence of tumor downstaging) were performed with the exact Wilcoxon test. Curves depicting correlation (Fig. 1) were obtained by fitting a logistic regression or Poisson regression model with three-knot restricted cubic splines [22]. p-values <.05 were considered statistically significant, and a p-value <.1 was reported as a nonstatistically significant trend.

Figure 1.

Figure 1.

Open in a new tab

Correlation of baseline soluble vascular endothelial growth factor receptor 1 (sVEGFR-1) concentration with pathological downstaging in rectal cancer after bevacizumab with chemoradiation. Shown are relationships between baseline sVEGFR-1 and the probabilities of complete pathological response (ypT0) and stage T3 residual disease (ypT3). The nonlinear curve was estimated by fitting logistic regression with restricted cubic splines, after double-log transformation of sVEGFR-1 concentration. The superimposed rectangles depict the distribution of ypT grade of residual disease by tertile groups of sVEGFR-1 (i.e., <84 pg/ml, 84–154 pg/ml, and >154 pg/ml). Points and triangles represent sVEGFR-1 measurements from patients who had a less than complete (ypT1–3) and complete (ypT0) pathological response, respectively (one measurement of >6 ng/ml not shown).

Results

Neoadjuvant Treatment Outcome

Tumor regression data after neoadjuvant therapy with bevacizumab and chemoradiation in protocol NCI #5642 were reported elsewhere [9]. Mandard grades of the primary tumor and the adverse events in these patients also were reported elsewhere.

Differential Biomarker Changes in Plasma and Urine

Concentrations of both VEGF and PlGF increased significantly in plasma at all time points analyzed during bevacizumab treatment alone (days 3 and 12) and after bevacizumab with chemoradiation (day 32 and presurgery) [9] (see supplemental online Fig. S1A, S1B for analyte kinetics in individual patients). However, no significant changes in either VEGF or PlGF were detectable in urine samples (data normalized to creatinine levels, supplemental online Fig. S2A, S2B). In addition, there was a transient increase in sVEGFR-2 and a transient decrease in sVEGFR-1 in plasma at day 3 after bevacizumab, which was not detectable at later time points during treatment or presurgery [9] (supplemental online Fig. S1C, S1D). Similar to VEGF and PlGF, we detected no significant change in urinary sVEGFR-1 at any of these time points (supplemental online Fig. S2C).

Plasma Versus Urinary Biomarker Correlations with Tumor Response: Role of Plasma sVEGFR-1

Biomarker analysis was performed for baseline values, for early changes after bevacizumab treatment alone (at days 3 and 12), and for concentration after bevacizumab with chemoradiation (at day 32) or prior to surgery (6 weeks after completion of neoadjuvant treatment). We explored the association between these biomarkers and tumor regression after therapy evaluated at surgery by tumor (T) restaging (ypT stage), Mandard scoring (which may reflect more accurately the primary tumor response [23]), or lymph nodal (N) staging at surgery.

Of 32 treated patients, five showed ypT0, five showed ypT1, six showed ypT2, and 16 showed ypT3 [9]. Of all four biomarkers measured at baseline in plasma and in urine, only plasma sVEGFR-1 concentration correlated directly with ypT stage at surgery (p < .05) (Table 1 and data not shown). Consistent with this finding, a high baseline plasma sVEGFR-1 level significantly correlated with a higher Mandard score (p < .01) (Table 1). Of interest, a high baseline plasma sVEGFR-1 level was also significantly associated with disease persistence after treatment (p < .01) and showed a nonstatistically significant trend for correlation with lack of T downstaging (p < .1) (supplemental online Table S1). None of the baseline biomarkers correlated with post-treatment N stage or N downstaging (Table 1 and supplemental online Table S1). Further analysis showed that, among 15 patients with plasma sVEGFR-1 concentrations less than the median value of 127 pg/ml, five (33%) had complete pathological regression (Mandard grade 1 and ypT0), versus 38% of patients with baseline sVEGFR-1 >127 pg/ml (Fig. 1). None of the baseline biomarkers measured in urine showed a significant association with tumor regression (Table 1 and supplemental online Table S1).

Table 1.

Correlation between plasma and urinary soluble vascular endothelial growth factor receptor 1 (sVEGFR-1) concentration and tumor regression after bevacizumab with chemoradiation in patients with locally advanced rectal cancer

graphic file with name onc00610-0601-t01.jpg

Open in a new tab

aData are shown as ρ values with 95% confidence intervals in square brackets. Positive values of Spearman's ρ indicate a direct correlation between a higher stage/score and higher biomarker levels (at baseline) or higher biomarker levels after treatment (relative to baseline); p-values are from the test of ρ = 0.

Of the biomarkers measured during treatment with bevacizumab alone, the extent of the decrease in plasma sVEGFR-1 at day 3 tended to associate with higher ypT stage after treatment (p < .1) (Table 1). Of note, the drop in plasma sVEGFR-1 at day 3 correlated with the absence of T and N downstaging (p < .05) (supplemental online Table S1). At day 12 after bevacizumab alone, the extent of the decrease in plasma sVEGFR-1 directly correlated with higher Mandard grade (p < .05) (Table 1). In addition, the drop in plasma sVEGFR-1 at day 12 showed a tendency for association with the absence of T and N downstaging (p < .1). Changes in urinary sVEGFR-1, PlGF, or VEGF after bevacizumab treatment alone showed no significant association with tumor regression (Table 1, supplemental online Table S1, and data not shown).

Of the plasma biomarkers measured during and after treatment with bevacizumab and chemoradiation, only the extent of the decrease in the concentration of sVEGFR-1 at day 32 significantly correlated with N downstaging (p < .05), and it tended to associate with T downstaging after treatment (p < .1) (supplemental online Table S1). Urinary sVEGFR-1 levels at day 32 inversely correlated with Mandard grade (p < .05) (Table 1). Neither plasma nor urinary sVEGFR-1 concentration presurgery correlated with any measure of treatment outcome (Table 1 and supplemental online Table S1). Of the other three biomarkers (VEGF, PlGF, sVEGFR-2) evaluated at these time points, the only correlation detected was between the higher concentration of plasma sVEGFR-2 presurgery and T downstaging after treatment.

Plasma sVEGFR-1 Is a Potential Biomarker of Toxicity

For toxicities, we explored the association between circulating biomarkers at baseline and their change after bevacizumab alone at days 3 and 12. The biomarkers were evaluated for associations with all adverse events during therapy and prior to surgery or with more serious adverse events (i.e., grade 3; there were no grade 4 adverse events recorded [9]).

Of all biomarkers evaluated at baseline, only plasma sVEGFR-1 inversely correlated with the number of all acute toxicities per patient and with the number of grade 3 toxicities per patient during therapy and prior to surgery (p < .05) (Table 2). Patients with higher sVEGFR-1 levels had a lower rate of adverse events: for example, there were no grade 3 adverse events among patients with a baseline sVEGFR-1 concentration ≥165 pg/ml, but grade 3 adverse events occurred in 16 of the 24 patients (73%) with baseline sVEGFR-1 concentrations <165 pg/ml (Fig. 2).

Table 2.

Correlation between plasma and urinary soluble vascular endothelial growth factor receptor 1 (sVEGFR-1) concentration and toxicity of bevacizumab with chemoradiation in patients with locally advanced rectal cancer

graphic file with name onc00610-0601-t02.jpg

Open in a new tab

aData are shown as ρ values with 95% confidence intervals in square brackets. Negative values of Spearman's ρ indicate an inverse correlation between a higher rate of adverse events and higher biomarker levels (at baseline) or higher biomarker levels after treatment (relative to baseline); p-values are from the test of ρ = 0.

Figure 2.

Figure 2.

Open in a new tab

Correlation of soluble vascular endothelial growth factor receptor 1 (sVEGFR-1) concentration with grade 3 adverse events (AEs) in rectal cancer patients after bevacizumab with chemoradiation. (A, B): Relationships between baseline sVEGFR-1 and mean number of adverse events per patient reported during chemoradiation treatment (A) and the probability of occurrence of grade 3 toxicities (B). The nonlinear curve was estimated by Poisson regression (A) or by fitting logistic regression (B) with restricted cubic splines, after double-log transformation of sVEGFR-1 concentration.

Of all the biomarkers evaluated after bevacizumab alone, only the extent of the decrease in plasma sVEGFR-1 at day 3 showed an association with the number of grade 3 toxicities (p < .05). No association was seen for plasma biomarker changes at day 12 and no significant correlation was seen for urinary biomarkers (Table 2).

Discussion

There are currently no validated biomarkers to select patients for bevacizumab treatment. The concentration of circulating VEGF, the target of bevacizumab therapy, has not been shown to be predictive of outcome. In this study, we evaluated the concentration of two members of the VEGF family and their receptors in plasma and urine, and explored their association with outcome and toxicity. The critical finding in this study is the striking association of pretreatment plasma sVEGFR-1 with both treatment response and toxicity. Plasma sVEGFR-1 correlated with both primary tumor response and toxicity after neoadjuvant bevacizumab-based chemoradiation. These data suggest that patients with high concentrations of plasma sVEGFR-1 (e.g., >175 pg/ml)—and potentially lower concentrations of VEGF signaling and VEGF-induced abnormal tumor vasculature—may experience fewer adverse events but might not benefit from bevacizumab therapy with cytotoxics. This further implies that sVEGFR-1 may potentially be used as a negative selection biomarker. This paradigm has proven to be useful with the use of anti–epidermal growth factor receptor agents, which appear to be ineffective in patients with KRAS-mutated colorectal cancer cells or in patients who do not experience toxicities such as skin rash (a potential “biomarker” of drug activity). For example, in studies of patients with metastatic rectal and colon cancer receiving cetuximab and cytotoxic chemotherapy, identification of KRAS mutation status as a predictive biomarker has led to the indication for cetuximab therapy only in patients with wild-type KRAS tumors [24, 25]. Baseline sVEGFR-1 concentration in plasma should be further explored as a strong candidate to determine the appropriate cutoff values and whether it could provide similarly useful information in estimating the likelihood of response to anti-VEGF therapy with bevacizumab in rectal cancer patients, and potentially in other cancers.

When evaluated during treatment, the early changes in plasma sVEGFR-1 were associated with tumor downstaging and with more severe adverse events after bevacizumab with chemoradiation. Thus, although anti-VEGF therapy changed all four plasma biomarkers evaluated by us, sVEGFR-1 may play a more important role in the antitumor and systemic effects of this therapy. These preliminary observations should be explored in larger studies to gain further mechanistic insight and validate the biomarker value of changes in sVEGFR-1 concentration.

Another important finding of this study is that changes in plasma circulating VEGF, PlGF, and sVEGFR-1 are not detectable in urine samples. Moreover, urinary sVEGFR-1 concentration at baseline or during treatment did not appear to associate with treatment response or toxicity.

In summary, the incorporation of bevacizumab and other anti-VEGF agents in the early treatment of cancer patients would be significantly enhanced by discovery of biomarkers that can be used to establish rational guidelines for the selection and use of these agents. Our study strongly supports the future exploration of baseline sVEGFR-1 as a predictive biomarker for therapies that include bevacizumab.

Supplementary Material

Supplemental Data
supp_15_6_577__index.html (1.2KB, html)

Acknowledgments

We thank Kathryn Kinzel for technical support. This study was partially supported by NIH grants R21-CA99237, P01-CA80124, R01-CA115767, R01-CA85140, and R01-CA126642 and Federal Share/NCI Proton Beam Program Income grants, and by the National Foundation for Cancer Research.

Author Contributions

Conception/Design: Dan G. Duda, Christopher G. Willett, Jeffrey W. Clark, Rakesh K. Jain

Financial support: Christopher G. Willett, Rakesh K. Jain

Administrative support: Christopher G. Willett, Rakesh K. Jain

Provision of study material or patients: Dan G. Duda, Christopher G. Willett, Gregory Lauwers, Jeffrey W. Clark, Rakesh K. Jain, Brian Czito, Paul Shellito

Collection and/or assembly of data: Dan G. Duda, Christopher G. Willett, Gregory Lauwers, Jeffrey W. Clark, Madeline Carroll, Douglas Tyler, Christopher Mantyh, Marek Ancukiewicz, Emmanuelle di Tomaso, Mira Shah, Brian Czito, Rex Bentley, Paul Shellito, Martin Poleski

Data analysis and interpretation: Dan G. Duda, Christopher G. Willett, Gregory Lauwers, Jeffrey W. Clark, Rakesh K. Jain, Douglas Tyler, Christopher Mantyh, Marek Ancukiewicz, Emmanuelle di Tomaso, Mira Shah, Brian Czito, Rex Bentley, Martin Poleski

Manuscript writing: Dan G. Duda, Christopher G. Willett, Rakesh K. Jain, Marek Ancukiewicz

Final approval of manuscript: Dan G. Duda, Christopher G. Willett, Gregory Lauwers, Jeffrey W. Clark, Madeline Carroll, Rakesh K. Jain, Douglas Tyler, Christopher Mantyh, Marek Ancukiewicz, Emmanuelle di Tomaso, Mira Shah, Brian Czito, Rex Bentley, Paul Shellito, Martin Poleski

References

  • 1.Sauer R, Becker H, Hohenberger W, et al. Preoperative versus postoperative chemoradiotherapy for rectal cancer. N Engl J Med. 2004;351:1731–1740. doi: 10.1056/NEJMoa040694. [DOI] [PubMed] [Google Scholar]
  • 2.Giantonio BJ, Catalano PJ, Meropol NJ, et al. Bevacizumab in combination with oxaliplatin, fluorouracil, and leucovorin (FOLFOX4) for previously treated metastatic colorectal cancer: Results from the Eastern Cooperative Oncology Group Study E3200. J Clin Oncol. 2007;25:1539–1544. doi: 10.1200/JCO.2006.09.6305. [DOI] [PubMed] [Google Scholar]
  • 3.Hurwitz H, Fehrenbacher L, Novotny W, et al. Bevacizumab plus irinotecan, fluorouracil, and leucovorin for metastatic colorectal cancer. N Engl J Med. 2004;350:2335–2342. doi: 10.1056/NEJMoa032691. [DOI] [PubMed] [Google Scholar]
  • 4.Dvorak HF. Vascular permeability factor/vascular endothelial growth factor: A critical cytokine in tumor angiogenesis and a potential target for diagnosis and therapy. J Clin Oncol. 2002;20:4368–4380. doi: 10.1200/JCO.2002.10.088. [DOI] [PubMed] [Google Scholar]
  • 5.Ferrara N, Gerber HP, LeCouter J. The biology of VEGF and its receptors. Nat Med. 2003;9:669–676. doi: 10.1038/nm0603-669. [DOI] [PubMed] [Google Scholar]
  • 6.Jain RK, Duda DG, Clark JW, et al. Lessons from phase III clinical trials on anti-VEGF therapy for cancer. Nat Clin Pract Oncol. 2006;3:24–40. doi: 10.1038/ncponc0403. [DOI] [PubMed] [Google Scholar]
  • 7.Crane CH, Eng C, Feig BW, et al. Phase II trial of neoadjuvant bevacizumab, capecitabine, and radiotherapy for locally advanced rectal cancer. Int J Radiat Oncol Biol Phys. 2010;76:824–830. doi: 10.1016/j.ijrobp.2009.02.037. [DOI] [PubMed] [Google Scholar]
  • 8.DiPetrillo TA, Pricolo V, Sikov WM, et al. Neoadjuvant bevacizumab, oxaliplatin, 5-fluorouracil, and radiation in clinical stage II-III rectal cancer. J Clin Oncol. 2008;26(15 suppl) doi: 10.1016/j.ijrobp.2010.08.005. Abstract 15041. [DOI] [PubMed] [Google Scholar]
  • 9.Willett CG, Duda DG, di Tomaso E, et al. Efficacy, safety, and biomarkers of neoadjuvant bevacizumab, radiation therapy, and fluorouracil in rectal cancer: A multidisciplinary phase II study. J Clin Oncol. 2009;27:3020–3026. doi: 10.1200/JCO.2008.21.1771. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Jain RK, Duda DG, Willett CG, et al. Biomarkers of response and resistance to antiangiogenic therapy. Nat Rev Clin Oncol. 2009;6:327–338. doi: 10.1038/nrclinonc.2009.63. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Chan LW, Moses MA, Goley E, et al. Urinary VEGF and MMP levels as predictive markers of 1-year progression-free survival in cancer patients treated with radiation therapy: A longitudinal study of protein kinetics throughout tumor progression and therapy. J Clin Oncol. 2004;22:499–506. doi: 10.1200/JCO.2004.07.022. [DOI] [PubMed] [Google Scholar]
  • 12.Izumi Y, Xu L, di Tomaso E, et al. Tumor biology: Herceptin acts as an anti-angiogenic cocktail. Nature. 2002;416:279–280. doi: 10.1038/416279b. [DOI] [PubMed] [Google Scholar]
  • 13.Jain RK. A new target for tumor therapy. N Engl J Med. 2009;360:2669–2671. doi: 10.1056/NEJMcibr0902054. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Plotkin SR, Stemmer-Rachamimov AO, Barker FG, 2nd, et al. Hearing improvement after bevacizumab in patients with neurofibromatosis type 2. N Engl J Med. 2009;361:358–367. doi: 10.1056/NEJMoa0902579. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Jain RK. Normalization of tumor vasculature: An emerging concept in antiangiogenic therapy. Science. 2005;307:58–62. doi: 10.1126/science.1104819. [DOI] [PubMed] [Google Scholar]
  • 16.Willett CG, Boucher Y, di Tomaso E, et al. Direct evidence that the VEGF-specific antibody bevacizumab has antivascular effects in human rectal cancer. Nat Med. 2004;10:145–147. doi: 10.1038/nm988. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Willett CG, Boucher Y, Duda DG, et al. Surrogate markers for antiangiogenic therapy and dose-limiting toxicities for bevacizumab with radiation and chemotherapy: Continued experience of a phase I trial in rectal cancer patients. J Clin Oncol. 2005;23:8136–8139. doi: 10.1200/JCO.2005.02.5635. [DOI] [PubMed] [Google Scholar]
  • 18.Mazzone M, Dettori D, Leite de Oliveira R, et al. Heterozygous deficiency of PHD2 restores tumor oxygenation and inhibits metastasis via endothelial normalization. Cell. 2009;136:839–851. doi: 10.1016/j.cell.2009.01.020. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Fischer C, Jonckx B, Mazzone M, et al. Anti-PlGF inhibits growth of VEGF(R)-inhibitor-resistant tumors without affecting healthy vessels. Cell. 2007;131:463–475. doi: 10.1016/j.cell.2007.08.038. [DOI] [PubMed] [Google Scholar]
  • 20.Fischer C, Mazzone M, Jonckx B, et al. FLT1 and its ligands VEGFB and PlGF: Drug targets for anti-angiogenic therapy? Nat Rev Cancer. 2008;8:942–956. doi: 10.1038/nrc2524. [DOI] [PubMed] [Google Scholar]
  • 21.Hoshida T, Sunamura M, Duda DG, et al. Gene therapy for pancreatic cancer using an adenovirus vector encoding soluble flt-1 vascular endothelial growth factor receptor. Pancreas. 2002;25:111–121. doi: 10.1097/00006676-200208000-00001. [DOI] [PubMed] [Google Scholar]
  • 22.Durrleman S, Simon R. Flexible regression models with cubic splines. Stat Med. 1989;8:551–561. doi: 10.1002/sim.4780080504. [DOI] [PubMed] [Google Scholar]
  • 23.Mandard AM, Dalibard F, Mandard JC, et al. Pathologic assessment of tumor regression after preoperative chemoradiotherapy of esophageal carcinoma. Clinicopathologic correlations. Cancer. 1994;73:2680–2686. doi: 10.1002/1097-0142(19940601)73:11<2680::aid-cncr2820731105>3.0.co;2-c. [DOI] [PubMed] [Google Scholar]
  • 24.Tol J, Koopman M, Cats A, et al. Chemotherapy, bevacizumab, and cetuximab in metastatic colorectal cancer. N Engl J Med. 2009;360:563–572. doi: 10.1056/NEJMoa0808268. [DOI] [PubMed] [Google Scholar]
  • 25.Van Cutsem E, Köhne CH, Hitre E, et al. Cetuximab and chemotherapy as initial treatment for metastatic colorectal cancer. N Engl J Med. 2009;360:1408–1417. doi: 10.1056/NEJMoa0805019. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplemental Data
supp_15_6_577__index.html (1.2KB, html)
supp_15.6.577_Supplemental_Data_Willett.pdf (823.3KB, pdf)
supp_15.6.577_Supplementary_Table_S1.pdf (19.2KB, pdf)

Articles from The Oncologist are provided here courtesy of Oxford University Press

RESOURCES