Although most investigations show a higher frequency of PTEN mutation when compared to allelic loss [18,38,39], Pollack et al. performed a sequence analysis of the nine exons of PTEN in a series of 62 malignant gliomas and found mutation in only one case, while PTEN allelic imbalance was detected in 7 of 22 cases (31.8%) [40], which is consistent with our findings. This evidence concerns the gene PTEN and malignant glioma.