RTOG 0525: Molecular correlates from a randomized phase III trial of newly diagnosed glioblastoma

LBA2000

Background: Formalin-fixed, paraffin embedded GBM tumor tissue, adequate for conventional MGMT methylation analyses, was required for entry onto the RTOG 0525 clinical trial. Methods: Four prognostic biomarkers were evaluated on a training set of 220 retrospectively obtained GBM samples, consisting of IDH1 mutation, the glioma-CpG island methylator phenotype (G-CIMP), a microarray-based mRNA panel and a novel MGMT promoter methylation assay. For each biomarker, 2 (IDH1 and mRNA) or 3 subgroups (G-CIMP and MGMT) were defined based on associations with overall survival. All combinations (36 possible) of each of the 4 biomarker-derived subgroups were then defined and compared with survival data and then consolidated into 4 risk groups. Once created in the training set, this model was applied to the RTOG 0525 samples (n=763) for external validation. Results: Application of the molecular risk classification to RTOG 0525 samples (left table) showed a highly significant survival association (p<0.001). When compared to the recursive partitioning analysis (RPA, table on right), this composite molecular classifier better identified patients with long term survival and appears to improve resolution by revealing an additional distinct risk group. The molecular classifier was prognostic in each of the treatment arms individually. Conclusions: Four distinct biomarkers or biomarker panels were tested in GBM. These biomarkers were compared with clinical outcome in a training set to optimize a method to combine them into a classifier. This classifier was then validated on a large sample set from a large phase III clinical trial. This composite panel may represent an improvement over the existing RPA with respect to risk stratification of patients for GBM. Additionally, it has the potential to impact future clinical trial designs and provide enhanced opportunities for personalization of therapy for GBM. Support: NCI U10 CA2121661, U10 CA37422, P50 CA127001.

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RTOG 0625: A phase II study of bevacizumab with irinotecan in recurrent glioblastoma (GBM)

2011

Background: Angiogenesis is a hallmark of GBM, making the tumor vasculature an attractive therapeutic target. In gliomas, vascular endothelial growth factor (VEGF) promotes both angiogenesis and invasion of tumor cells. Bevacizumab is a humanized monoclonal antibody against VEGF-A that rapidly reduces the concentration of VEGF in the circulation. Irinotecan may enhance efficacy by synergistic tumor endothelial cell death or improved tumor delivery of the chemotherapy via “normalized” tumor vasculature. Prior studies of this combination demonstrated high radiographic response and 6-month progression free (6-mPFS) rates. This study was designed to determine the efficacy and safety of this regimen in the cooperative group setting. Methods: Eligibility included age ≥ 18, centrally confirmed GBM or gliosarcoma, progressive or recurrent disease. Enzyme-inducing anticonvulsants were not allowed. Treatment was intravenous bevacizumab 10 mg/kg and irinotecan 200 mg/m2 every 2 weeks. Accrual goal was 57 eligible patients. Primary endpoint was 6-mPFS rate where an estimate of ≥ 35% would define efficacy (15% improvement over historical data). Results: Full enrollment (57) was achieved, median age was 57, median KPS was 80; all had prior radiation and temozolomide treatment. The 6m-PFS rate was 37% (95% CI: 24–50%), with 21 of 57 patients progression-free at 6 months. Moderate toxicity was noted with 21(37%) grade 3, seven (12%) grade 4, and one (<2%) treatment-related death (intracranial hemorrhage). There were six episodes of venous thrombosis, 14 episodes of grade 3 or 4 hematologic toxicity, predominantly lymphopenia (7), and neutropenia (4), no opportunistic infections or febrile neutropenia were noted. Other toxicities included fatigue (9), diarrhea (2), and hypertension (2). Conclusions: These results, in the cooperative group context, corroborate the efficacy of the bevacizumab and irinotecan combination for recurrent GBM with the 6m-PFS surpassing the predetermined efficacy threshold. Previously described toxicities were confirmed with a moderately high rate of venous thrombosis, one intracranial hemorrhage, and moderate hypertension. Studies to determine the contribution of the cytotoxic agent to efficacy and the role of bevacizumab in newly diagnosed GBM are planned.

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MGMT methylation testing in RTOG 0525: A phase III trial of newly diagnosed glioblastoma

2051

Background: MGMT promoter methylation has been described as a prognostic marker in glioblastoma (GBM) and may be associated with chemosensitivity to alkylating agents. This study determined the feasibility of real-time determination of MGMT promoter methylation testing in a large international phase III clinical trial. Methods: Paraffin tumor blocks were obtained from patients registered onto RTOG 0525 then distributed to one of two central pathology labs: MD Anderson (Houston TX, K. Aldape) or CHUV (Lausanne, CH, R. Janzer). After histologic confirmation of GBM, unstained slides (40 microns of tumor tissue) were sent to the testing laboratories. Results were used for randomization into a treatment arm. MGMT methylation was assessed using methylation specific real-time PCR (MSP). The assay determined the number of copies of both methylated MGMT and of beta-actin (ACTB) in the sample. The ACTB copy number was used to assess the quality and quantity of the sample DNA. Results: Results were available for 995 samples. Following MSP samples were categorized into one of five possible results: failed (2, 0.2%), methylated (302, 30.2%), non-methylated (602, 60.2%), indeterminate (62, 6.2%), and invalid (27, 2.7%). Among cases that were evaluable as either methylated or unmethylated (n = 904) the MGMT promoter methylation rate in newly diagnosed GBM was approximately 1/3 (33.4%), a rate that is somewhat lower than prior reports. The average time from receipt of sample at the central pathology laboratory to reporting of results was 9.3 days. The time required decreased over the course of the clinical trial. This was due, in part, to training of the sites to deliver samples just before the start of runs. Conclusions: The results demonstrate the feasibility of performing real-time MGMT methylation testing, a tumor based assay, as a stratification factor in a multinational clinical trial. This study confirms that treatment decisions based on the molecular characteristics of the tumor are feasible, thereby providing opportunities to develop more molecularly-based tumor stratification or selection, a major advance in developing personalized treatment regimens.

No significant financial relationships to disclose.