The SNPs selected for pharmacogenetic studies of bevacizumab have been diverse. Some studies have included a few SNPs in one gene, whereas others have assessed many SNPs across multiple genes. The most widely assessed gene is VEGFA
. High, although not 100%, linkage disequilibrium has been reported between the VEGFA
–2578 A, –1498 C, –1154 A, and –634 G alleles.21
Linkage disequilibrium is a higher frequency than expected of carriers of a combination of two or more alleles in a specific population. Thus, although the alleles are not interchangeable, correlations with one might represent a signal of uniformity with the others. Unfortunately, no causative SNPs have yet been identified, which could limit some of the congruence between trials. Studies have also involved a wide range of disease types and settings, efficacy phenotypes, and antiangio-genic drugs, and have varied in size. Comparisons of studies must, therefore, be viewed with caution. Despite these limitations, strengths of pharmacogenetic studies include that the genotype is constant and, therefore, independent of the time of collection, and that assays are technically simple and highly reproducible. Significant efficacy markers identified in pharmacogenetic correlative studies are shown in .
Efficacy markers in pharmacogenetic correlative substudies of antiangiogenic agents
Candidate SNPs were studied in the clinical E2100 phase 3 trial ().4
Patients received weekly paclitaxel with or without bevacizumab as first-line therapy for metastatic breast cancer. The addition of bevacizumab was associated with improved response rate and PFS (the primary endpoint), but not with improved overall survival. Common SNPs in the VEGFA
gene and its receptor, VEGFR2, were retrospectively studied.22,43
SNPs were all in regulatory regions (no common non-synonymous polymorphisms have been found in VEGFA
) and all had a high minor allele frequency. VEGFA
–2578 AA and –1154 AA genotypes were associated with better median overall survival than other genotypes. Similar effects were seen for PFS but were non-significant. No such effect was seen in the control groups, which suggests that these SNPs had predictive value.
In the AVADO trial,5
docetaxel alone or with 7·5 mg/kg or 15·0 mg/kg bevacizumab were assessed as first-line treatments for metastatic breast cancer (). The AVADO investigators studied 26 SNPs across 13 genes important for regulation of the VEGFA
pathway, hypertension, and inflammation.23
Median PFS was improved in carriers of the VEGFA
–2578 A allele who received docetaxel plus 7·5 mg/kg bevacizumab, but not in those who received docetaxel alone or with 15·0 mg/kg bevacizumab. PFS was also improved in patients with the VEGFA –
634 CC genotype who received docetaxel alone, but not in those who received bevacizumab, which suggests a prognostic effect. No correlation was seen between overall survival and any of the SNPs tested.
The Hellenic Cooperative Oncology Group did a correlative study on their phase 3 trial findings for bevacizumab with either FOLFIRI (leucovorin, fluorouracil, and irinotecan) or XELIRI (irinotecan and capecitabine).24
The genotypes VEGFA
–2578 CC and –1154 GG correlated with shortened overall survival ().25
This finding is similar in direction to that in the E2100 trial where the alternate genotypes (VEGFA
–2578 AA and –1154 AA) were associated with improved overall survival. A marginal improvement in PFS was also associated with the VEGFA
–1154 AA genotype, and the greater effect on overall survival than on PFS supports the findings of the E2100 trial. Although the exaggerated effect on overall survival (compared with that for PFS) could clearly be due to chance, it might reflect biological changes that occur after disease progression, as has been seen in some preclinical models.44,45
Another small cohort study assessed FOLFIRI with bevacizumab as first-line therapy in 40 patients with metastatic colorectal cancer26
and investigated correlations between median PFS and VEGFA
SNPs. Improved PFS correlated with the VEGFA
–1154 AA genotype. A correlation was also seen between the VEGFA
–634 GG genotype and improved response rate ().
The E4599 trial27
was a phase 3 study that assessed bevacizumab in the treatment of metastatic lung cancer. 878 patients were randomly assigned paclitaxel and carboplatin alone or with bevacizumab. Median overall survival and PFS were better in the bevacizumab group than in the group that received paclitaxel and carboplatin alone. In a correlative substudy in 133 patients,28
SNPs in nine genes that regulate angiogenesis and inflammation were assessed. An SNP profile or signature (as opposed to an individual SNP) of VEGFA
469T/C, and IL8
–251T/A was the best predictor of overall survival and PFS (). Of note, the VEGFA
–634 G allele, which was seen in the profile associated with improved outcomes, is in linkage disequilibrium with the VEGFA
–1154 A and –2578 A alleles that correlated with improved outcome in E2100.
Similar pathway approaches were implemented in a phase 2 study of low-dose cyclophosphamide plus bevacizumab to treat metastatic ovarian cancer.29
53 (76%) of 70 patients had SNP biomarkers assessed. The investigators selected SNPs across 30 genes. For VEGFA
, only the –634 C/G and the 936 C/T SNPs were assessed. Decreased response was correlated with the IL8
–251 A allele and improved PFS with the CXCR2
785 CC or CT and VEGFA
936 CT genotypes (). This trial, however, was limited by small sample size and multiple comparisons, although the selections of genes and SNPs were extensive.
The AViTA trial30
was a phase 3 trial done in patients with metastatic pancreatic cancer who were randomly assigned gemcitabine and erlotinib, alone or with bevacizumab. Of the 607 patients enrolled, 154 (25%) had samples available for SNP analysis.31
157 SNPs in the angiogenesis pathway were assessed. Correlations were seen between a VEGFR1
(also known as FLT1
) SNP (rs9582036) and improved overall survival and PFS in patients who received bevacizumab (). The investigators subsequently studied another VEGFR1
SNP (rs7993418) that had functional implications and was in full linkage disequilibrium with rs9582036 in the AVOREN trial. In AVOREN, an association was found with improved PFS but not overall survival. No correlation was seen between the VEGFA
–2578 AA genotype and outcome.
The similar findings from two independent phase 3 studies (the Hellenic Cooperative Oncology Group and E2100 studies) provide strong evidence that SNPs in VEGFA
have predictive value as biomarkers for response to bevacizumab. The strength of the relation is tempered by the lack of correlation in the AVADO study,5
despite the disease type (breast cancer) and setting being similar to those in E2100. Docetaxel in AVADO was associated with less benefit with bevacizumab than was paclitaxel in E2100. The lack of concordance in the AViTA trial31
is less concerning, as patients in that study had pancreatic cancer and the addition of bevacizumab added no benefit. Although in a negative trial a biomarker can identify a subgroup of patients who will benefit, if the agent being assessed has little or no effect, the likelihood of a biomarker being useful diminishes. The discovery of a VEGFR1
SNP, however is provocative, and if replicated will deserve attention. The results from the E4599 trial28
provide some additional support for the correlations seen with VEGFA
, but the findings are inadequate to draw firm conclusions. Additionally, the development of a multigene SNP signature makes comparison with the findings of other studies difficult. The level of evidence for the use of VEGFA
SNPs in the clinical setting is inadequate, but further study is clearly warranted.