When we compared the percent change in Gd-DTPA AUC of each bradykinin B2 receptor agonist group to that of the NS group, we found that there was a statistically significant tumor volume effect on the percent change in Gd-DTPA AUC in anterior brain tumors, but not in the case of posterior brain RG-2 gliomas, which were smaller and had a narrower range of tumor volume distributions than the anterior brain RG-2 gliomas in the study (Additional file 1). This evidence concerns the gene BDKRB2 and central nervous system cancer.