Chromosomal instability in oral premalignancy

Kim, Jae Seok; Kim, Hyo Jin

Abstract

BACKGROUND: Squamous cell carcinoma of the oral cavity was thought to develop through a multistep process driven by genetic changes. Recently, the use of in situ hybridization on paraffin sections has been reported, thus allowing one to visualize specific chromosomal changes without disrupting the spatial distributions of such changes in the tissue samples. Specific aims of this study were to determine whether genetic alterations are present in premalignant oral lesions, i.e. leukoplakia and to examine whether the degree of genetic alterations is associated with risk of cancer development.
METHODS
Twenty-eight formalin fixed, paraffin- embedded specimens were obtained from 26 patients with oral leukoplakia at the University of Texas MD Anderson Cancer Center. The 6-micron thick tissue sections were mounted on glass slides precoated with silane or poly-l- lysine. The tissue sections were baked at 65oC overnight and deparaffinized in xylene-ethanol series. And then presoaked in cold pepsin/HCl solution for 15 minutes and incubated with 0.4% pepsin in 0.2N HCl at 37oC for 10-45 minutes. The biotinylated centromeric DNA probe specific for chromosome 17 and target DNA were denatured together at 90oC-95oC for 4-7 minutes and incubated at 37oC overnight in sealed wet chamber. The tissue sections were stained with immunoperoxidase technique using avidin-biotin-peroxidase enzyme complex and diaminobenzidine as a substrate. The tissue sections were counterstained with Giemsa stain. At least, 200 nuclei were scored in each slide. The total number of signal spots were divided by the number of nuclei analyzed to obtain a chromosome index. The cells with > or = 3 chromosome copies were divided by the total counting cells to obtain the degree of chromosomal polysomy.
RESULTS
Chromosomal polysomy was more prevalent in dysplastic lesions (median 8.1%, range 0.5-23.0%) than lesions without dysplasia (median 3.0%, range 0-14.5%). Interestingly, 6/17 cases exhibiting >2.0% polysomy subsequently developed invasive carcinoma or carcinoma in situ compared to 0/11 cases with low or no polysomy. There was clear association between chromosome index and the degree of chromosomal polysomy. CONCLUSON: Oral premalignant lesions had genetic alterations. Dysplastic lesions habor more genetic changes than hyperplastic lesions. Risk of oral cancer development seems to be associated with cummulative genetic changes. There was clear association between chromosome index and the degree of baseline chromosomal polysomy. These results suggest that the degree of chromosomal instability present in premalignant oral lesions is associated with the risk of cancer development.