Extensive intra-tumor heterogeneity in primary human glial tumors as a result of locus non-specific genomic alterations

Genomic changes are a hallmark of the neoplastic process. These range from alterations at specific loci and defined karyotypic changes which influence tumor behavior to generalized alterations exemplified by microsatellite in stability. Generalized genomic changes within a tumor would be evidence in favor of the mutator hypothesis which postulates a role for such extensive changes during tumorigenesis. In this report, we have used the DNA fingerpr inting technique of randomly amplified polymorphic DNA (RAPD) analysis to s tudy genomic alterations within primary human astrocytic tumors (gliomas) i n a locus non-specific manner. The RAPD fingerprinting profile of consecuti ve segments of tumors 2 mm across was studied; 17 astrocytic (high- and low -grade) tumors were sectioned end to end. Tissue from 50 consecutive sectio ns, 40 mu m thick (total 2 mm across), was pooled and taken to be a tumor c ompartment. DNA was subjected to RAPD amplification by 15 random 10-mer pri mers. A tumor segment was taken to have a DNA fingerprinting pattern different fr om others in the same specimen when its RAPD profile differed from others b y at least one band of one RAPD reaction. All but one of the tumors showed compartments with a unique genetic profile, indicating genomic instability leading to widespread intra-tumor genetic heterogeneity. Eight tumors were also studied for loss of heterozygosity (LOH) of the p53 and D17S379 loci i n the different segments as examples of alteration of specific tumor influe ncing loci. Three showed LOH of p53, which was limited to only one compartm ent of each tumor. The extensive intra-tumor genetic instability detected in this study is sug gestive of the overall high rate of change in the genomes of tumors includi ng those of a lower grade. It is hypothesized that some of these altered cl ones, which manifest as zones of heterogeneity in a solid tumor, may accumu late changes at loci known to influence tumor behavior, and thus clinical o utcome.