Similar BCL-X but different BCL-2 levels in the two age groups of north African nasopharyngeal carcinomas

Nasopharyngeal carcinomas (NPCs) are consistently associated with the Epstein–Barr virus (EBV). As Bcl-2 and Bcl-X are co-expressed in EBV-transformed B-lymphocytes, we attempted to determine their status in malignant NPC cells. A retrospective series of 100 NPC specimens from untreated Tunisian patients was investigated by immuno-histochemistry. Twenty seven of the patients were below 30 years old and therefore classified in the “juvenile” form of north African NPCs. Bcl-2 and Bcl-X expression was assessed semi-quantitatively using a score based on the percentage of positive cells and staining intensity. Intense Bcl-X expression was detected in malignant cells of 100% biopsy samples with similar scores for patients below 30 years or those aged 30 or over. Bcl-2 was detected in 89% biopsies but its expression differed considerably between the samples. The average Bcl-2 score was much lower for patients under 30 years (4.4±1.5 compared to 6.5±2 for older patients; P<10−6). Multivariate analysis demonstrated that no other clinical parameter, except the primary tumor size, was correlated to the Bcl-2 score. Bcl-X and Bcl-2 are co-expressed in 89% of NPCs whereas their expression is mutually exclusive in other head and neck carcinomas (particularly squamous cell carcinomas, SCC). The constantly high expression of Bcl-X is consistent with it being induced by the EBV protein Epstein–Barr nuclear antigen 1 (EBNA1), as recently reported in a murine model. The contrasted levels of Bcl-2 expression in the two age groups strengthen the hypothesis that these clinical forms result from distinct oncogenic mechanisms.