ABSTRACT
Oral squamous cell carcinoma [OSCC] is considered the sixth most common malignancy , and a major cause of cancer morbidity and mortality world wide. One of the capabilities required for carcinogensis is evasion of apoptosis .This involves normal alteration in the Fas [Apo-1/ CD95] receptor ligand apoptotic pathway . Apoptosis is a physiological cell death , it plays a significant role in the pathogenesis of various diseases and tumors and also plays the main role in killing of cancer cells by chemo and radiotherapy. Twenty two cases of OSCC were studied in this research for the expression of both antigens Fas and Fas-L ligand .The correlation of their expression with the histopathological grading and with the immune escape behavior of the OSCC was the aim of this work. The correlation between the pattern of expression of Fas and the three histopathological grades of OSCC was highly significant [p< 0.004]. The apoptotic Fas receptor showed downregulation as we move to the high grade of OSCC. This results point out that it is one the of hallmark of immune escape behavior of OSCC. The altered expression of Fas antigen can be used as a marker for dys-plastic and premalignant changes. It is a prognostic factor for tumor aggressive behavior and as a predictor factor for response to chemo or radiotherapy. Primary tumors negative for the Fas-L is one of the immune escape policies of OSCC since its presence only attacks neutrophils Fas -L tumor cell expression is a late step in tumor progression and is mostly demonstrated in metastatic cases