METHODS: Fifty-three formalin-fixed, paraffin-embedded nasopharyngeal carcinoma tissue blocks were chosen for this study. The presence of Epstein-Barr virus (EBV) was determined by in situ hybridisation using an EBER probe. p53 protein expression was detected using immunohistochemistry. Simultaneously, amplifications by PCR were performed for p53 exons 5 to 8, followed by mutation screening via single strand conformation polymorphism (SSCP). Sequencing of all the four exons was performed in five samples with mobility shift. To rule out false negative results by SSCP, 13 samples with p53 overexpression and five samples with low p53 expression were randomly selected and sequenced.
RESULTS: There was no mutation found in exons 5 to 8 in all the samples despite 46 (87%) of them having high p53 levels. EBV was detected in 51 (96%) out of 53 samples. There was no statistically significant association between p53 expression level and EBV presence.
CONCLUSIONS: High-intensity staining for p53 by immunohistochemistry was common in our series of NPC tissue samples but was not associated with 'hot spot' mutations of exons 5-8 of the gene. We did not find a significant relationship between the expression level of p53 and presence of EBV. Our study confirms that mutation of the DNA-binding domain of p53 is rare in NPC.