The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein, with an extracellular ligand-binding domain and intracellular tyrosine kinase domain. Ligand binding induces EGFR dimerization and autophosphorylation on several tyrosine residues in the intracellular domain, leading to mitogenic signal transduction. EGFR overexpression correlates with a poor prognosis and is often associated with malignant transformation in a variety of epithelial cancers. ABX-EGF is a high-affinity (dissociation constant K(D) = 5 x 10(-11) M) fully human IgG2 monoclonal antibody against human EGFR. ABX-EGF binds EGFR and blocks receptor binding of EGF and transforming growth factor-alpha, inhibiting EGFR tyrosine phosphorylation and tumor cell activation. ABX-EGF prevents tumor formation and eradicates large, established A431 tumors in xenograft models. Tumor growth inhibition occurs at relatively low doses, without concomitant chemotherapy or radiotherapy. When combined with chemotherapeutic agents, ABX-EGF has resulted in additive antitumor activity. A Phase I clinical trial has demonstrated activity in several tumor types, and the results from a Phase II trial for renal cell cancer also showed modest activity. Therapy was generally well tolerated without statistically significant adverse events. Monoclonal antibody blockade of EGFR represents a new and exciting direction in cancer therapy.

Background

The prognostic significance of baseline contrast enhancing tumor prior to second- or third-line therapy in recurrent glioblastoma (GBM) for overall survival (OS) remains controversial, particularly in the context of repeated surgical resection and/or use of anti-angiogenic therapy. In the current study, we examined recurrent GBM patients from both single and multicenter clinical trials to test whether baseline enhancing tumor volume, including central necrosis, is a significant prognostic factor for OS in recurrent GBM.

Methods

Included were 497 patients with recurrent GBM from 4 data sources: 2 single-center sites (University of Toronto, University of California Los Angeles) and 2 phase II multicenter trials (AVF3708G, Bevacizumab ± Irinotecan, NCT00345163; XL184-201, Cabozantinib, NCT00704288). T1 subtraction maps were used to define volume of contrast enhancing tumor, including central necrosis. Cox multivariable and univariate analyses were used to evaluate the relationship between tumor volume prior to second- or third-line therapy and OS.

Results

Both continuous measures of baseline tumor volume and tumors dichotomized into large (≥15cc) and small (<15cc) tumors were significant predictors of OS (P<.0001), independently of age and treatment. Univariate analysis demonstrated significant OS differences (P<.05) between large (≥15cc) and small (<15cc) tumors in patients under all therapeutic scenarios. Only patients treated with cabozantinib who previously failed anti-angiogenic therapy did not show an OS dependence on baseline tumor volume.

Conclusions

Baseline tumor volume is a significant prognostic factor in recurrent GBM. Clinical trial treatment arms must have a balanced distribution of tumor size, and tumor size should be considered when interpreting therapeutic efficacy.

Background

To overcome challenges with traditional response assessment in anti-angiogenic agents, the current study uses T1 subtraction maps to quantify volumetric radiographic response in monotherapy with cabozantinib, an orally bioavailable tyrosine kinase inhibitor with activity against vascular endothelial growth factor receptor 2 (VEGFR2), hepatocyte growth factor receptor (MET), and AXL, in an open-label, phase II trial in patients with recurrent glioblastoma (GBM) (NCT00704288).

Methods

A total of 108 patients with adequate imaging data and confirmed recurrent GBM were included in this retrospective study from a phase II multicenter trial of cabozantinib monotherapy (XL184-201) at either 100 mg (N = 87) or 140 mg (N = 21) per day. Contrast enhanced T1-weighted digital subtraction maps were used to define volume of contrast-enhancing tumor at baseline and subsequent follow-up time points. Volumetric radiographic response (>65% reduction in contrast-enhancing tumor volume from pretreatment baseline tumor volume sustained for more than 4 wk) was tested as an independent predictor of overall survival (OS).

Results

Volumetric response rate for all therapeutic doses was 38.9% (41.4% and 28.6% for 100 mg and 140 mg doses, respectively). A log-linear association between baseline tumor volume and OS (P = 0.0006) and a linear correlation between initial change in tumor volume and OS (P = 0.0256) were observed. A significant difference in OS was observed between responders (median OS = 20.6 mo) and nonresponders (median OS = 8.0 mo) (hazard ratio [HR] = 0.3050, P < 0.0001). Multivariable analyses showed that continuous measures of baseline tumor volume (HR = 1.0233, P < 0.0001) and volumetric response (HR = 0.2240, P < 0.0001) were independent predictors of OS.

Conclusions

T1 subtraction maps provide value in determining response in recurrent GBM treated with cabozantinib and correlated with survival benefit.

Purpose: Anti-VEGF therapies remain controversial in the treatment of recurrent glioblastoma (GBM). In the current study, we demonstrate that recurrent GBM patients with a specific diffusion MR imaging signature have an overall survival (OS) advantage when treated with cediranib, bevacizumab, cabozantinib, or aflibercept monotherapy at first or second recurrence. These findings were validated using a separate trial comparing bevacizumab with lomustine.Experimental Design: Patients with recurrent GBM and diffusion MRI from the monotherapy arms of 5 separate phase II clinical trials were included: (i) cediranib (NCT00035656); (ii) bevacizumab (BRAIN Trial, AVF3708g; NCT00345163); (iii) cabozantinib (XL184-201; NCT00704288); (iv) aflibercept (VEGF Trap; NCT00369590); and (v) bevacizumab or lomustine (BELOB; NTR1929). Apparent diffusion coefficient (ADC) histogram analysis was performed prior to therapy to estimate "ADC_L," the mean of the lower ADC distribution. Pretreatment ADC_L, enhancing volume, and clinical variables were tested as independent prognostic factors for OS.Results: The coefficient of variance (COV) in double baseline ADC_L measurements was 2.5% and did not significantly differ (P = 0.4537). An ADC_L threshold of 1.24 μm²/ms produced the largest OS differences between patients (HR ∼ 0.5), and patients with an ADC_L > 1.24 μm²/ms had close to double the OS in all anti-VEGF therapeutic scenarios tested. Training and validation data confirmed that baseline ADC_L was an independent predictive biomarker for OS in anti-VEGF therapies, but not in lomustine, after accounting for age and baseline enhancing tumor volume.Conclusions: Pretreatment diffusion MRI is a predictive imaging biomarker for OS in patients with recurrent GBM treated with anti-VEGF monotherapy at first or second relapse. Clin Cancer Res; 23(19); 5745-56. ©2017 AACR.