Evidence of genetic instability in tumors and normal nearby tissues.

Background: Comprehensive analyses have recently been performed on many human cancer tissues, leading to the identification of a number of mutated genes but providing no information on the variety of mutations present in each of them. This information is of interest to understand the possible origin of gene mutations that cause tumors.

Methodology/principal Findings: We have analyzed the sequence heterogeneity of the transcripts of the human HPRT and G6PD single copy genes that are not considered tumor markers.