CYTOGENETIC EVIDENCE OF THE MULTISTEP ORIGIN OF HEAD AND NECK SQUAMOUS-CELL CARCINOMAS

Background: Head and neck squamous cell carcinomas are associated with tobacco and alcohol use; therefore, the incidence of this type of tumor is expected to rise in the future as a result of the increasing numbers of female and adolescent smokers. Previous reports of cytogenetic analysis of this type of tumor have implicated a number of chromosomal regions in recurring changes, but no clear pattern of characteristic changes has emerged. Purpose: We have undertaken cytogenetic analysis of 10 cell lines which were established from squamous cell carcinomas of the head and neck, to determine the possible sites of additional tumor suppressor genes and oncogenes that may contribute to malignant transformation. Methods: Metaphases were harvested from cultures of cells in the exponential growth phase, following exposure to Colcemid (demecolcine) at a final concentration of 30 ng/mL, for 5 hours. Air-dried slides were G-banded using trypsin and Giemsa. Fifteen metaphases were photographed and fully karyotyped. Results: We observed that several chromosomal regions were lost at high frequency, including 18q (10 of 10 lines), 10p (eight of 10 lines), 3p (six of 10 lines), 8p (seven of 10 lines), and the short arms of the acrocentric chromosomes (seven of 10 lines). Nine of 10 lines had additional copies of 7p. We also noted clustering of break-points in a number of chromosome bands, including 1p22, 10q11.2, 11q13, and the short arms of the acrocentric chromosomes. Conclusion: The observation of loss of multiple chromosomal regions in a significant number of lines analyzed is consistent with the theory that tumorigenesis occurs as the result of the accumulation of a number of genetic alterations, as proposed for colorectal carcinoma. The high frequency with which these changes are seen suggests that genes located in these regions have a role in the etiology of this type of tumor.