Drugs that target blood vessels in malignant brain tumours

Background
The commonest primary brain tumours of adults are gliomas which comprise about two-fifths of all primary brain tumours. Gliomas span a spectrum from low to high grade, and are graded pathologically on a scale of one to four, according to a classification by the World Health Organization (WHO) that was last updated in 2016. High-grade glioma, including glioblastoma, are difficult to treat and carry a poor prognosis.

These tumours produce a protein that promotes the formation of new blood vessels (angiogenesis) to help them grow. Drugs have been developed to reduce the formation of new blood vessels and slow tumour growth. Bevacizumab, cediranib and cilengitide are anti-angiogenic drugs that directly or indirectly target blood vessel formation and have been studied in glioblastoma in randomised clinical trials. 

Study characteristics
After a comprehensive search up to October 2018, we identified 11 eligible randomised clinical trials (totaling 3743 participants). All eligible studies were restricted to glioblastomas; there were no eligible studies that included other brain tumour types. The largest trials were conducted in newly diagnosed people with glioblastoma, treated with anti-angiogenic therapy. Overall, the trials included in this systematic review did not show improvement in overall survival with the use of anti-angiogenic therapy. Overall, the clinical trials in bevacizumab-treated glioblastoma did prolong the time until tumour growth (progression-free survival).

Key results
Anti-angiogenic therapy does not significantly prolong life in newly diagnosed people with glioblastoma. In recurrent glioblastoma although there is no evidence of prolonging life over chemotherapy, when anti-angiogenic therapies are used in combination with certain chemotherapy regimes there may be a small improvement in survival. Anti-angiogenic agents delay tumour progression on magnetic resonance imaging (MRI) scans but is commonly associated with side effects, such as high blood pressure and protein in the urine.

Authors' conclusions: 

The use of anti-angiogenic therapy does not significantly improve overall survival in newly diagnosed people with glioblastoma. Thus, there is insufficient evidence to support the use of anti-angiogenic therapy for people with newly diagnosed glioblastoma at this time. Overall there is a lack of evidence of a survival advantage for anti-angiogenic therapy over chemotherapy in recurrent glioblastoma. When considering the combination anti-angiogenic therapy with chemotherapy compared with the same chemotherapy alone, there may possibly be a small improvement in overall survival. While there is strong evidence that bevacizumab (an anti-angiogenic drug) prolongs progression-free survival in newly diagnosed and recurrent glioblastoma, the impact of this on quality of life and net clinical benefit for patients remains unclear. Not addressed here is whether subsets of people with glioblastoma may benefit from anti-angiogenic therapies, nor their utility in other HGG histologies.

Read the full abstract...
Background: 

This is an updated version of the original Cochrane Review published in September 2014. The most common primary brain tumours in adults are gliomas. Gliomas span a spectrum from low to high grade and are graded pathologically on a scale of one to four according to the World Health Organization (WHO) classification. High-grade glioma (HGG) carries a poor prognosis. Grade IV glioma is known as glioblastoma and carries a median survival in treated patients of about 15 months. Glioblastomas are rich in blood vessels (i.e. highly vascular) and also rich in a protein known as vascular endothelial growth factor (VEGF) that promotes new blood vessel formation (the process of angiogenesis). Anti-angiogenic agents inhibit the process of new blood vessel formation and promote regression of existing vessels. Several anti-angiogenic agents have been investigated in clinical trials, both in newly diagnosed and recurrent HGG, showing preliminary promising results. This review was undertaken to report on the benefits and harms associated with the use of anti-angiogenic agents in the treatment of HGGs.

Objectives: 

To evaluate the efficacy and toxicity of anti-angiogenic therapy in people with high-grade glioma (HGG). The intervention can be used in two broad groups: at first diagnosis as part of 'adjuvant' therapy, or in the setting of recurrent disease.

Search strategy: 

We conducted updated searches to identify published and unpublished randomised controlled trials (RCTs), including the Cochrane Central Register of Controlled Trials (CENTRAL; 2018, Issue 9), MEDLINE and Embase to October 2018. We handsearched proceedings of relevant oncology conferences up to 2018. We also searched trial registries for ongoing studies.

Selection criteria: 

RCTs evaluating the use of anti-angiogenic therapy to treat HGG versus the same therapy without anti-angiogenic therapy.

Data collection and analysis: 

Review authors screened the search results and reviewed the abstracts of potentially relevant articles before retrieving the full text of eligible articles.

Main results: 

After a comprehensive literature search, we identified 11 eligible RCTs (3743 participants), of which 7 were included in the original review (2987 participants). There was significant design heterogeneity in the included studies, especially in the response assessment criteria used. All eligible studies were restricted to glioblastomas and there were no eligible studies evaluating other HGGs. Ten studies were available as fully published peer-reviewed manuscripts, and one study was available in abstract form. The overall risk of bias in included studies was low. This risk was based upon low rates of selection bias, detection bias, attrition bias and reporting bias. The 11 studies included in this review did not show an improvement in overall survival with the addition of anti-angiogenic therapy (pooled hazard ratio (HR) of 0.95, 95% confidence interval (CI) 0.88 to 1.02; P = 0.16; 11 studies, 3743 participants; high-certainty evidence). However, pooled analysis from 10 studies (3595 participants) showed improvement in progression-free survival with the addition of anti-angiogenic therapy (HR 0.73, 95% CI 0.68 to 0.79; P < 0.00001; high-certainty evidence).

We carried out additional analyses of overall survival and progression-free survival according to treatment setting and for anti-angiogenic therapy combined with chemotherapy compared to chemotherapy alone. Pooled analysis of overall survival in either the adjuvant or recurrent setting did not show an improvement (HR 0.93, 95% CI 0.86 to 1.02; P = 0.12; 8 studies, 2833 participants; high-certainty evidence and HR 0.99, 95% CI 0.85 to 1.16; P = 0.90; 3 studies, 910 participants; moderate-certainty evidence, respectively). Pooled analysis of overall survival for anti-angiogenic therapy combined with chemotherapy compared to chemotherapy also did not clearly show an improvement (HR 0.92, 95% CI 0.85 to 1.00; P = 0.05; 11 studies, 3506 participants; low-certainty evidence). The progression-free survival in the subgroups all showed findings that demonstrated improvements in progression-free survival with the addition of anti-angiogenic therapy. Pooled analysis of progression-free survival in both the adjuvant and recurrent setting showed an improvement (HR 0.75, 95% CI 0.69 to 0.82; P < 0.00001; 8 studies, 2833 participants; high-certainty evidence and HR 0.64, 95% CI 0.54 to 0.76; P < 0.00001; 2 studies, 762 participants; moderate-certainty evidence, respectively). Pooled analysis of progression-free survival for anti-angiogenic therapy combined with chemotherapy compared to chemotherapy alone showed an improvement (HR 0.72, 95% CI 0.66 to 0.77; P < 0.00001; 10 studies, 3464 participants). Similar to trials of anti-angiogenic therapies in other solid tumours, adverse events related to this class of therapy included hypertension and proteinuria, poor wound healing, and the potential for thromboembolic events, although generally, the rate of grade 3 and 4 adverse events was low (< 14.1%) and in keeping with the literature. The impact of anti-angiogenic therapy on quality of life varied between studies.

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