Visualization of the timing of gene amplification during multistep head and neck tumorigenesis

Head and neck tumorigenesis is thought to represent a multistep process whe reby carcinogen exposure leads to genetic instability in the tissue and the accumulation of specific genetic events, which result in dysregulation of proliferation, differentiation, and cell loss and the acquisition of invasi ve capacity. Chromosome 11q13 amplification Is frequently observed in head and neck squamous cell carcinoma (HNSCC), and the amplified gene products a re assumed to play important functional roles in the tumor phenotype. Howev er, it is not well understood whether gene amplification precedes carcinoma development or results from the unstable nature of intact tumors. To deter mine the timing of gene amplification during tumorigenesis, tissue sections from amplified HNSCC specimens (containing a contiguous transition from no rmal epithelium to hyperplasia to dysplasia to carcinoma) were probed for I NT2 gene copy number by chromosome in situ hybridization, In addition, repr esentative epithelia were microdissected from the tissue sections, and the DNA was isolated and assessed for INT2 gene copy number by semiquantitative PCR, In those cases containing amplified INT2 in the carcinoma, gene ampli fication appeared to precede HNSCC development. In one case, INT2 gene ampl ification appeared in the hyperplasia to dysplasia transition, whereas in t wo other cases, gene amplification was apparent at dysplasia. These results suggest that gene amplification can occur early during head and neck tumor igenesis and that genetic instability is an important driving force in the tumorigenesis process.