CELL CYCLE REGULATING GENES AND THEIR PROTEIN EXPRESSION IN SQUAMOUS CELL CARCINOMA OF THE LARYNX AND HYPOPHARYNX

Abstract

Background. The major mechanisms involved in genomic instability during tumour progression are loss of heterozygosity (LOH) and microsatellite instability (MSI). The most frequently affected are the tumor suppressor genes (TSG). Alterations of cell cycle proteins contribute to the development and biologic behaviour of malignant tumours. Methods. In a prospective study we evaluated the distribution and prognostic significance of immunohistochemically detected proteins p53, p21, p16, Rb, and cyclin D1 in 101 squamous cell carcinomas of the larynx and hypopharynx (LHSCC). Additionally, non isotopic MSI and LOH analysis was performed with microsatellite markers on chromosomes 3p, 9p, 17p, and 11q. Immunohistochemical and molecular alterations were compared to tumour grade, disease stage and three year patients’ overall and disease free survival. Results. Of 101 patients, there were 94 men and 7 women with 73 laryngeal and 28 hypopharyngeal cancers. Immunohistochemical staining was performed on all tumours and molecular analysis in 77 patients. In LHSCC, varying patterns of protein expression were found. A significant correlation was found between cyclin D1 and p21, cyclin D1 and Rb expression, and Rb expression and tumour grade. p53 and p16 expression did not correlate with other proteins. p16 expression correlated with LOH at 9p21, and LOH at 11q13 (cyclin D1 region) correlated with the tumour grade. We observed a high incidence of LOH at specific chromosomal regions: 3p (61%), 9p (54.4%), 17p (57.1%) and 11q (19.5%). Conversely, MSI was present in 6.5% of cases. In addition to tumour grade and N stage, only cyclin D1 expression revealed independent prognostic value for overall, but not disease free survival after multivariate analysis. Conclusions. In conclusion, our study demonstrated the derailment of the growth promoting and suppressing pathways of cell cycle control in almost all LHSCC. Our results suggest that Rb gene inactivation might also be important in the development of LHSCC. It appears that cyclin D1 has a central role in the regulation of the cell cycle in LHSCC. When over-expressed it is able to override most of the inhibitory action exercised by its antagonists and has an independent prognostic value for patient overall survival. Our study demonstrated that the TSG, involved in the regulation of the cell cycle, are changed significantly in LHSCC. The most important mechanism involved, compared to low MSI, appears to be LOH, indicating a dominant role of the suppressor pathway in LHSCC carcinogenesis.