Radiotherapy or Surgery of the Axilla After a Positive Sentinel Node in Breast Cancer: 10-Year Results of the Randomized Controlled EORTC 10981-22023 AMAROS Trial.

PURPOSE: The European Organisation for Research and Treatment of Cancer 10981-22023 AMAROS trial evaluated axillary lymph node dissection (ALND) versus axillary radiotherapy (ART) in patients with cT1-2, node-negative breast cancer and a positive sentinel node (SN) biopsy. At 5 years, both modalities showed excellent and comparable axillary control, with significantly less morbidity after ART. We now report the preplanned 10-year analysis of the axillary recurrence rate (ARR), overall survival (OS), and disease-free survival (DFS), and an updated 5-year analysis of morbidity and quality of life. METHODS: In this open-label multicenter phase III noninferiority trial, 4,806 patients underwent SN biopsy; 1,425 were node-positive and randomly assigned to either ALND (n = 744) or ART (n = 681). RESULTS: Per intention-to-treat analysis, 10-year ARR cumulative incidence was 0.93% (95% CI, 0.18 to 1.68; seven events) after ALND and 1.82% (95% CI, 0.74 to 2.94; 11 events) after ART (hazard ratio [HR], 1.71; 95% CI, 0.67 to 4.39). There were no differences in OS (HR, 1.17; 95% CI, 0.89 to 1.52) or DFS (HR, 1.19; 95% CI, 0.97 to 1.46). ALND was associated with a higher lymphedema rate in updated 5-year analyses (24.5% v 11.9%; P < .001). Quality-of-life scales did not differ by treatment through 5 years. Exploratory analysis showed a 10-year cumulative incidence of second primary cancers of 12.1% (95% CI, 9.6 to 14.9) after ART and 8.3% (95% CI, 6.3 to 10.7) after ALND. CONCLUSION: This 10-year analysis confirms a low ARR after both ART and ALND with no difference in OS, DFS, and locoregional control. Considering less arm morbidity, ART is preferred over ALND for patients with SN-positive cT1-2 breast cancer.

Phase 1 Study of Chemoradiotherapy Combined with Nivolumab ± Ipilimumab for the Curative Treatment of Muscle-invasive Bladder Cancer.

BACKGROUND: Muscle-invasive bladder cancer (MIBC) has a poor prognosis. Chemoradiotherapy (CRT) in selected patients has comparable results to radical cystectomy. Results of neoadjuvant immune checkpoint inhibitors (ICIs) before radical cystectomy are promising. We hypothesize that ICI concurrent to CRT (iCRT) is safe and may improve treatment outcomes. OBJECTIVE: To determine the safety of iCRT for MIBC. DESIGN, SETTING, AND PARTICIPANTS: This multicenter, phase 1b, open-label, dose-escalation study determined the safety of CRT with three ICI regimens in patients with nonmetastatic (T2-4aN0-1) MIBC. Twenty-six patients received mitomycin C/capecitabine and 20 × 2.75 Gy to the bladder. Tolerability was evaluated in a cohort of up to ten patients. If two or fewer out of the first six patients or three or fewer of ten patients experienced dose-limiting toxicity (DLT), accrual continued in the next cohort. INTERVENTION: Patients received nivolumab 480 mg (NIVO480), nivolumab 3 mg/kg and ipilimumab 1 mg/kg (NIVO3 + IPI1), or nivolumab 1 mg/kg and ipilimumab 3 mg/kg (IPI3 + NIVO1). OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary endpoint was safety. Secondary objectives were response rate, disease-free survival, metastatic-free survival (MFS), and overall survival (OS). RESULTS AND LIMITATIONS: In the NIVO480 cohort, no patients experienced DLT. The NIVO3 + IPI1 2 patients experienced DLT, thrombocytopenia (grade 4), and asystole (grade 5). IPI3 + NIVO1 was discontinued after three out of six patients experienced DLT. Clinically significant adverse events (AEs) of grade ≥3 occurred in zero, three, and five patients in the NIVO480, NIVO3 + IPI1, and IPI3 + NIVO1 groups, respectively. The most common AEs were immune related and gastrointestinal. MFS and OS were 90% at 2 yr for NIVO480 and 90% at 1 yr for NIVO3 + IPI1. Limitations include the absence of a centralized pathology and radiology review, and a lack of biomarker analysis. CONCLUSIONS: In this dose-finding study of iCRT, the regimens of nivolumab monotherapy and nivolumab 3 mg/kg with ipilimumab 1 mg/kg have acceptable toxicity. PATIENT SUMMARY: We tested the safety of a new bladder-sparing treatment modality for muscle-invasive bladder cancer patients, combining immune checkpoint inhibitors simultaneously with chemoradiotherapy. We report that two regimens, nivolumab monotherapy and nivolumab 3 mg/kg with ipilimumab 1 mg/kg, are safe and can be used in phase 3 trials.

Gross tumour volume delineation in anal cancer on T2-weighted and diffusion-weighted MRI - Reproducibility between radiologists and radiation oncologists and impact of reader experience level and DWI image quality.

PURPOSE: To assess how gross tumour volume (GTV) delineation in anal cancer is affected by interobserver variations between radiologists and radiation oncologists, expertise level, and use of T2-weighted MRI (T2W-MRI) vs. diffusion-weighted imaging (DWI), and to explore effects of DWI quality. METHODS AND MATERIALS: We retrospectively analyzed the MRIs (T2W-MRI and b800-DWI) of 25 anal cancer patients. Four readers (Senior and Junior Radiologist; Senior and Junior Radiation Oncologist) independently delineated GTVs, first on T2W-MRI only and then on DWI (with reference to T2W-MRI). Maximum Tumour Diameter (MTD) was calculated from each GTV. Mean GTVs/MTDs were compared between readers and between T2W-MRI vs. DWI. Interobserver agreement was calculated as Intraclass Correlation Coefficient (ICC), Dice Similarity Coefficient (DSC) and Hausdorff Distance (HD). DWI image quality was assessed using a 5-point artefact scale. RESULTS: Interobserver agreement between radiologists vs. radiation oncologists and between junior vs. senior readers was good-excellent, with similar agreement for T2W-MRI and DWI (e.g. ICCs 0.72-0.94 for T2W-MRI and 0.68-0.89 for DWI). There was a trend towards smaller GTVs on DWI, but only for the radiologists (P = 0.03-0.07). Moderate-severe DWI-artefacts were observed in 11/25 (44%) cases. Agreement tended to be lower in these cases. CONCLUSION: Overall interobserver agreement for anal cancer GTV delineation on MRI is good for both radiologists and radiation oncologists, regardless of experience level. Use of DWI did not improve agreement. DWI artefacts affecting GTV delineation occurred in almost half of the patients, which may severely limit the use of DWI for radiotherapy planning if no steps are undertaken to avoid them.

MRI-Based Upper Abdominal Organs-at-Risk Atlas for Radiation Oncology.

PURPOSE: The purpose of our study was to provide a guide for identification and contouring of upper abdominal organs-at-risk (OARs) in the setting of online magnetic resonance imaging (MRI)-guided radiation treatment planning and delivery. METHODS AND MATERIALS: After a needs assessment survey, it was determined that an upper abdominal MRI-based atlas of normal OARs would be of benefit to radiation oncologists and radiation therapists. An anonymized diagnostic 1.5T MRI from a patient with typical upper abdominal anatomy was used for atlas development. Two MRI sequences were selected for contouring, a T1-weighted gadoxetic acid contrast-enhanced MRI acquired in the hepatobiliary phase and axial fast imaging with balanced steady-state precession. Two additional clinical MRI sequences from commercial online MRI-guided radiation therapy systems were selected for contouring and were included in the final atlas. Contours from each data set were completed and reviewed by radiation oncologists, along with a radiologist who specializes in upper abdominal imaging, to generate a consensus upper abdominal MRI-based OAR atlas. RESULTS: A normal OAR atlas was developed, including recommendations for contouring. The atlas and contouring guidance are described, and high-resolution MRI images and contours are displayed. OARs, such as the bile duct and biliary tree, which may be better seen on MRI than on computed tomography, are highlighted. The full DICOM/DICOM-RT MRI images from both the diagnostic and clinical online MRI-guided radiation therapy systems data sets have been made freely available, for educational purposes, at econtour.org. CONCLUSIONS: This MRI contouring atlas for upper abdominal OARs should provide a useful reference for contouring and education. Its routine use may help to improve uniformity in contouring in radiation oncology planning and OAR dose calculation. Full DICOM/DICOM-RT images are available online and provide a valuable educational resource for upper abdominal MRI-based radiation therapy planning and delivery.

[Axillary lymph node dissection versus axillary radiotherapy in patients with a positive sentinel node: the AMAROS trial]. / Okselklierdissectie versus okselbestraling bij borstkankerpatiënten met een positieve schildwachtklier: de EORTC 10981 AMAROS-studie.

OBJECTIVE: To investigate whether axillary radiotherapy (ART) in patients with primary breast cancer and a tumour-positive sentinel node results in a similar axillary tumour recurrence rate compared with axillary lymph node dissection (ALND), and whether ART results in lower morbidity. DESIGN: Randomised, multicentre non-inferiority trial. METHOD: Patients with breast cancer ≤ 5 cm without clinical signs of lymph node metastases but with a tumour-positive sentinel node were randomised between ALND or ART. The primary endpoint was the 5-year axillary recurrence rate. Secondary endpoints were disease-free survival, overall survival, morbidity (lymphoedema and shoulder function) and quality of life. (www.clinicaltrials.gov, study number NCT00014612.) RESULTS: Between 2001 and 2010, 1425 patients with a tumour-positive sentinel node were included, 744 of whom had been randomised to ALND and 681 to ART. After a median follow-up period of 6.1 years, the 5-year axillary recurrence rate was 0.43% after ALND and 1.19% after ART; the difference was not statistically significant. The primary analysis was underpowered due to the low number of axillary recurrences. At 5 years the disease-free survival rate was 86.9% after ALND and 82.7% after ART. Overall survival was 93.3% and 92.5% respectively. Lymphoedema was noted significantly more often after ALND than after ART at 1 year, 3 years and 5 years. There were no significant differences in shoulder function or quality of life. CONCLUSION: Both ART and ALND produce very low axillary recurrence rates in patients with breast cancer ≤ 5 cm and a tumour-positive sentinel node. ART results in significantly less lymphoedema than ALND.

Is axillary lymph node clearance required in node-positive breast cancer?

Although the majority of patients with breast cancer have clinically negative axillary nodes at preoperative assessment, around 15-20% of these women will have metastatic disease within the lymph nodes at operative sentinel node biopsy, and additional selective treatment to the axilla might be required. Local treatment to the axilla can include axillary node clearance or axillary radiotherapy. The recent results of the American College of Surgeons Oncology Group Z0011 trial suggested that some women would be safe from recurrence without further axillary treatment if they have less than three involved sentinel nodes, with no extracapsular spread. We review the evidence base for management of the axilla after detection of a positive sentinel node, discuss the evidence for why micrometastatic disease requires systemic but not axillary therapy, and present data suggesting that axillary irradiation for macrometastases gives equivalent control to axillary node clearance, but causes less morbidity such as lymphoedema. Ongoing trials will confirm whether any further therapy can be omitted for all patients with low volume, sentinel-node macrometastases.

Marking axillary lymph nodes with radioactive iodine seeds for axillary staging after neoadjuvant systemic treatment in breast cancer patients: the MARI procedure.

OBJECTIVE: The MARI procedure [marking the axillary lymph node with radioactive iodine (I) seeds] is a new minimal invasive method to assess the pathological response of nodal metastases after neoadjuvant systemic treatment (NST) in patients with breast cancer. This method allows axilla-conserving surgery in patients responding well to NST. METHODS: Prior to NST, proven tumor-positive axillary lymph nodes were marked with a I seed. This marked lymph node is the so-called MARI-node. After NST, the MARI node was selectively removed using a γ-detection probe. A complementary axillary lymph node dissection was performed in all patients to assess whether pathological response in the MARI node was indicative for the pathological response in the additional lymph nodes. RESULTS: A tumor-positive axillary lymph node was marked with a I seed in 100 patients. The MARI node was successfully identified in 97 of these 100 patients (identification rate 97%). Two patients did not undergo subsequent axillary lymph node dissection, leaving 95 patients for further analysis. The MARI node contained residual tumor cells in 65 of these 95 patients. In the other 30 patients, the MARI node was free of tumor, but additional positive lymph nodes were found in 5 patients. Thus, the MARI procedure correctly identified 65 of 70 patients with residual axillary tumor activity (false negative rate 5/70 = 7%). CONCLUSIONS: This study shows that marking and selectively removing metastatic lymph nodes after neoadjuvant systemic treatment has a high identification rate and a low false negative rate. The tumor response in the marked lymph node may be used to tailor further axillary treatment after NST.

Radiotherapy or surgery of the axilla after a positive sentinel node in breast cancer (EORTC 10981-22023 AMAROS): a randomised, multicentre, open-label, phase 3 non-inferiority trial.

BACKGROUND: If treatment of the axilla is indicated in patients with breast cancer who have a positive sentinel node, axillary lymph node dissection is the present standard. Although axillary lymph node dissection provides excellent regional control, it is associated with harmful side-effects. We aimed to assess whether axillary radiotherapy provides comparable regional control with fewer side-effects. METHODS: Patients with T1-2 primary breast cancer and no palpable lymphadenopathy were enrolled in the randomised, multicentre, open-label, phase 3 non-inferiority EORTC 10981-22023 AMAROS trial. Patients were randomly assigned (1:1) by a computer-generated allocation schedule to receive either axillary lymph node dissection or axillary radiotherapy in case of a positive sentinel node, stratified by institution. The primary endpoint was non-inferiority of 5-year axillary recurrence, considered to be not more than 4% for the axillary radiotherapy group compared with an expected 2% in the axillary lymph node dissection group. Analyses were by intention to treat and per protocol. The AMAROS trial is registered with ClinicalTrials.gov, number NCT00014612. FINDINGS: Between Feb 19, 2001, and April 29, 2010, 4823 patients were enrolled at 34 centres from nine European countries, of whom 4806 were eligible for randomisation. 2402 patients were randomly assigned to receive axillary lymph node dissection and 2404 to receive axillary radiotherapy. Of the 1425 patients with a positive sentinel node, 744 had been randomly assigned to axillary lymph node dissection and 681 to axillary radiotherapy; these patients constituted the intention-to-treat population. Median follow-up was 6·1 years (IQR 4·1-8·0) for the patients with positive sentinel lymph nodes. In the axillary lymph node dissection group, 220 (33%) of 672 patients who underwent axillary lymph node dissection had additional positive nodes. Axillary recurrence occurred in four of 744 patients in the axillary lymph node dissection group and seven of 681 in the axillary radiotherapy group. 5-year axillary recurrence was 0·43% (95% CI 0·00-0·92) after axillary lymph node dissection versus 1·19% (0·31-2·08) after axillary radiotherapy. The planned non-inferiority test was underpowered because of the low number of events. The one-sided 95% CI for the underpowered non-inferiority test on the hazard ratio was 0·00-5·27, with a non-inferiority margin of 2. Lymphoedema in the ipsilateral arm was noted significantly more often after axillary lymph node dissection than after axillary radiotherapy at 1 year, 3 years, and 5 years. INTERPRETATION: Axillary lymph node dissection and axillary radiotherapy after a positive sentinel node provide excellent and comparable axillary control for patients with T1-2 primary breast cancer and no palpable lymphadenopathy. Axillary radiotherapy results in significantly less morbidity. FUNDING: EORTC Charitable Trust.

Breast-conserving treatment with or without radiotherapy in ductal carcinoma In Situ: 15-year recurrence rates and outcome after a recurrence, from the EORTC 10853 randomized phase III trial.

PURPOSE: Adjuvant radiotherapy (RT) after a local excision (LE) for ductal carcinoma in situ (DCIS) aims at reduction of the incidence of a local recurrence (LR). We analyzed the long-term risk on developing LR and its impact on survival after local treatment for DCIS. PATIENTS AND METHODS: Between 1986 and 1996, 1,010 women with complete LE of DCIS less than 5 cm were randomly assigned to no further treatment (LE group, n = 503) or RT (LE+RT group, n = 507). The median follow-up time was 15.8 years. RESULTS: Radiotherapy reduced the risk of any LR by 48% (hazard ratio [HR], 0.52; 95% CI, 0.40 to 0.68; P < .001). The 15-year LR-free rate was 69% in the LE group, which was increased to 82% in the LE+RT group. The 15-year invasive LR-free rate was 84% in the LE group and 90% in the LE+RT group (HR, 0.61; 95% CI, 0.42 to 0.87). The differences in LR in both arms did not lead to differences in breast cancer-specific survival (BCSS; HR, 1.07; 95% CI, 0.60 to 1.91) or overall survival (OS; HR, 1.02; 95% CI, 0.71 to 1.44). Patients with invasive LR had a significantly worse BCSS (HR, 17.66; 95% CI, 8.86 to 35.18) and OS (HR, 5.17; 95% CI, 3.09 to 8.66) compared with those who did not experience recurrence. A lower overall salvage mastectomy rate after LR was observed in the LE+RT group than in the LE group (13% v 19%, respectively). CONCLUSION: At 15 years, almost one in three nonirradiated women developed an LR after LE for DCIS. RT reduced this risk by a factor of 2. Although women who developed an invasive recurrence had worse survival, the long-term prognosis was good and independent of the given treatment.

Comparison of the sentinel node procedure between patients with multifocal and unifocal breast cancer in the EORTC 10981-22023 AMAROS Trial: identification rate and nodal outcome.

INTRODUCTION: Multifocal breast cancer is associated with a higher risk of nodal involvement compared to unifocal breast cancer and the drainage pattern from multifocal localisations may be different. For this reason, the value of the sentinel node biopsy (SNB) procedure for this indication is debated. The aim of the current analysis was to evaluate the sentinel node identification rate and nodal involvement in patients with a multifocal tumour in the EORTC 10981-22023 AMAROS trial. PATIENTS AND METHODS: From the first 4000 registered patients, 342 were identified with a multifocal tumour on histological examination and compared to a randomly selected control group of 684 patients with a unifocal tumour. The outcome of the SNB was assessed. RESULTS: The sentinel node was identified in 96% of the patients with a multifocal tumour and in 98% of those with unifocal disease. In the multifocal group, 51% had a metastasis in the sentinel node compared to 28% in the unifocal group; and further nodal involvement after a positive sentinel node was found in 40% (38/95) and 39% (39/101) respectively. CONCLUSION: In this prospective international multicentre study, the 96% detection rate indicates that the SNB procedure can be highly effective in patients with a multifocal tumour. Though the tumour-positive rate of the sentinel node was twice as high in the multifocal group compared to the unifocal group, further nodal involvement after a positive sentinel node was similar in both groups. This suggests that the SNB procedure is safe in patients with multifocal breast cancer.

Guiding breast-conserving surgery in patients after neoadjuvant systemic therapy for breast cancer: a comparison of radioactive seed localization with the ROLL technique.

BACKGROUND: Radioguided occult lesion localization (ROLL) with technetium-99 m colloid (ROLL-(99m)Tc) is commonly used to perform breast-conserving surgery in patients with nonpalpable breast tumors. Radioactive seed localization is a relatively new technique that localizes the tumor with a radioactive iodine-125 ((125)I) seed. The feasibility and outcome of these techniques after neoadjuvant systemic treatment has not been widely investigated. METHODS: All patients treated with neoadjuvant systemic treatment between 2007 and 2010 in the Netherlands Cancer Institute who underwent breast-conserving surgery with the ROLL-(99m)Tc technique (n = 83) or with (125)I seed localization (n = 71) were analyzed. The weight of the resected specimen, the margins, and the percentage of patients requiring a second surgical intervention as a result of positive margins were assessed. RESULTS: Patient and tumor characteristics and systemic treatment regimens were comparable between both groups. The median weight of the resected specimen (53 vs. 48 g), the median smallest margin (3.5 vs. 3.0 mm), and the risk for additional surgery for incomplete resections (7 vs. 8 %) did not differ significantly between patients treated with the ROLL-(99m)Tc technique and (125)I seed localization. CONCLUSIONS: The ROLL-(99m)Tc technique and (125)I seed localization demonstrate comparable results when used to perform breast-conserving surgery after neoadjuvant systemic treatment. Because (125)I seed localization does not require additional radiological localization shortly before surgery, it simplifies surgery scheduling. Therefore, we prefer (125)I seed localization to perform breast-conserving surgery after neoadjuvant systemic treatment.

[Local recurrence after skin-sparing mastectomy]. / Lokaal recidief na huidsparende ablatio mammae.

On average, 250 skin-sparing mastectomies with immediate prosthetic reconstruction are performed in the Dutch Antoni van Leeuwenhoek Hospital each year. We report on two breast cancer patients (46 and 53 years old) who each developed a local recurrence at the entry site of the core needle biopsy after skin-sparing mastectomy with immediate prosthetic reconstruction. In hindsight, the most likely cause for these recurrences was the fact that one of the entry sites for the core needle biopsies was not marked preoperatively, and thus not excised during surgery. These examples emphasise the need for accurate documentation of the locations of these entry sites, followed by their excision, in patients undergoing skin-sparing mastectomy for invasive breast cancer.

Angiogenesis inhibitor DC101 delays growth of intracerebral glioblastoma but induces morbidity when combined with irradiation.

The combination of irradiation with angiogenic inhibition is increasingly being investigated for treatment of glioblastoma multiforme (GBM). We investigated whether vascular endothelial growth factor receptor-2 (VEGFR-2) inhibitor DC101 affects morbidity and tumor growth in irradiated and non-irradiated intracerebral GBM-bearing mice, controlled with sham treatments. End-points were toxicity, morbidity and histology. Irradiation either or not combined, reduced tumor size strongly, whereas DC101 mono-treatment reduced tumor size by 64%. Irradiation delayed morbidity from 5.8 weeks in sham-treated mice to 10.3 weeks. Morbidity after combined treatment occurred after 5.9 weeks. Treatment with angiogenesis inhibitor DC101 delays tumor growth but it induces morbidity, by itself or combined with irradiation.

Characterization of structurally distinct, isoform-selective phosphoinositide 3'-kinase inhibitors in combination with radiation in the treatment of glioblastoma.

The phosphoinositide 3'-kinase (PI3K)-mediated signaling pathway plays a key role in fundamental cellular functions important in normal cellular homeostasis and malignant transformation. Deregulated signaling through this pathway contributes to development of gliomas and their resistance to radiation and chemotherapy. Targeting the PI3K signaling pathway has thus emerged as a promising approach to successful treatment of gliomas. We assessed the radiosensitizing potential of four small-molecule inhibitors that differ in their activities against specific isoforms of the PI3K 110-kDa catalytic subunit (p110). p110alpha inhibitors blocked phosphorylation of both protein kinase B/Akt and S6 in all cell lines examined, effectively decreased cellular proliferation, and produced additive cytotoxic effects in combination with radiation therapy. The p110beta inhibitor exhibited limited biochemical effects and failed to decrease cellular proliferation or viability as either a single agent or in combination with radiation or rapamycin. In vivo studies examining the effects of the p110alpha inhibitor in combination with radiation indicated a significant reduction in tumor growth rate induced by the combined treatment compared with each treatment modality alone. This translated into a trend toward prolonged time-to-failure for mice in the combination treatment group. In conclusion, PI3K inhibitors are promising agents in the treatment of glioblastomas, especially when used in combination with ionizing radiation.

Negligible radiation protection of endothelial cells by vascular endothelial growth factor.

Glioblastoma multiforme (GBM) is a radioresistant tumor. Tumor neoangiogenesis is an important mechanism for tumor sustenance. Angiogenesis is primarily mediated by vascular endothelial growth factor (VEGF), and earlier studies have suggested that VEGF protects human umbilical vein endothelial cells (HUVECs) against high doses of radiation. We tried to extend these findings to other endothelial cell lines and clinically relevant irradiation doses. Therefore, four different endothelial cell lines (HUVEC-C, primary HUVEC-P, an immortalized HUVEC cell line: EC-RF24, and bovine retina endothelial cells: BREC) were cultured without or with recombinant human VEGF165 (rhVEGF165). Cells were irradiated with gamma-rays from a 137Cs-source. Radiosensitivity was determined by proliferation or clonogenic assay. Apoptosis was assayed by flow cytometric determination of the sub-G1 population or by counting nuclear fragmentation. We found that the biologically active rhVEGF165 was able to improve clonogenic survival of HUVEC-C after 2 and 5 Gy. However, rhVEGF165 could not significantly alter the radiosensitivity of all cell lines studied in proliferation assays. rhVEGF165 only slightly reduced apoptosis in HUVEC-C after 3 Gy. In conclusion, the radioprotective effect from rhVEGF165 was found on different endothelial cell lines after clinically relevant radiation doses was negligible. We therefore hypothesize that the high VEGF-levels found in GBM in vivo do not reduce the radiosensitivity of endothelial cells, which is thought to contribute to the strong radioresistance of the tumor vasculature.