A total number of 317 consecutive patients with squamous cell carcinoma of the oral cavity were analysed by DNA flow cytometry. The proportion of tumors consisting exclusively of diploid cells decreased from 75% in T1G1 carcinomas to less than 10% in advanced tumors in favor of cases characterized by the presence of cell lines with aberrant DNA content. This observation indicates a genetic evolution of tumor clones with severe karyotype aberrations from diploid progenitors which obviously represents an ultimate event in the pathogenesis of oral carcinomas. Aneuploidy formation clearly contributes to the acquisition of progressive malignant behaviour as is underlined by a dramatic difference of the survival outcome of patients with diploid tumors (5-year overall survival: 88%) as compared to those who had aneuploid tumors (36%; P<0.001), a relationship which held true even if identical tumor stages were considered. There were no indications of successive genetic changes of the cellular DNA contents during tumor progression which would explain the wide range of variation of the individual DNA values. This observation supports the hypothesis of an aneuploidy formation by a single cytogenetic event, such as an abnormal mitosis. Although there were indications of an even worse survival outcome in the group of patients with peri-diploid tumor cell lines (P<0.1), a significant influence of different DNA contents on the prognosis could not be detected.

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