OBJECTIVEThe purpose of the study is to investigate the mechanism of immune escape and the expression of Fas and Fas L in oral premalignant lesions (OPLs) and oral squamous cell carcinomas (OSCCs).

METHODS64 samples, including normal oral mucosa(7), hyperkeratosis(9), premalignant lesions(24) and squamous cell carcinomas(24), were studied. The cells in the test specimens, which demonstrate granular staining, were considered as positive. The expression of Fas and Fas L was evaluated semi-quantitatively as follows: -, no expression; + (mild), < 5% positive cells; ++ (moderate), 6%-25% positive cells; +++ (intense), 26%-50% positive cells; or ++++ (very intense), > 50% positive cells.

RESULTSIn the process of oral carcinogenesis, each stage had Fas expression. The positive staining appeared essentially on cell membrane. Various degrees of Fas expression were seen in the diseased tissues. The number of positively stained cells in the moderately and severely dysplastic tissues appeared higher than that in the normal control (P < 0.05). In the OSCC group, the level of expression of Fas antigen decreased significantly by comparison with the normal controls (P < 0.05). Fas L expression was discovered in each stage of the process of oral carcinogenesis. The positive staining appeared in cytoplasm. In hyperkeratotic tissues and OPLs, the number of Fas L expression cells was significantly higher than that in the normal controls. The number of Fas L expression cells of OSCCs increased by comparison with both normal controls and OPLs.

CONCLUSIONThe results indicate that the expression of Fas and Fas L is involved in oral carcinogenesis and this may be directly related to the mechanism by which the cancer cells evade the host immune assault. Perhaps, Fas/Fas L system may be used as a prognostic biomarker in predicting the behavior of oral premalignant lesions in the near future.