[Correlation between Fas/Fas-ligand expression and apoptosis in undifferentiated nasopharyngeal carcinoma]

We determined whether resistance to Fas-mediated apoptosis is involved in the development of undifferentiated nasopharyngeal carcinomas (UNPCs). In UNPC tissue sections from 20 cases, we conducted immunohistochemistry to detect Fas and FasL, in situ hybridization to detect Epstein-Barr virus-encoded small RNA (EBER), and immunohistochemistry for single-stranded DNA (ssDNA) to detect apoptotic cells. Fas was detected in 17/20 (85%), FasL in 15/20 (75%), and EBER in 16/20 (80%). Fas was detected in all 16 EBER-positive UNPCs, but not in 3 (75%) of 4 EBER-negative UNPCs. FasL was detected in 12 (75%) of 16 EBER-positive UNPCs and 3 (75%) of 4 EBER-negative UNPCs. Interestingly, despite Fas and FasL co-expression in UNPC cells (Fas+/FasL+ cases = 13/20 or 65%), apoptotic UNPC cells were significantly lower in Fas+/FasL+ than in other cases. These results suggest that Fas+/FasL+ UNPC cells are resistant to Fas-mediated apoptosis in vivo by mechanisms excluding lack of Fas expression.