We studied 15 NPC cases to establish correlation between p53 expression, Ki-67 LI and histopathological subtypes. The tumor suppressor gene, p53, regulates cell proliferation and apoptosis. It is the most common mutation found in many cancers. P53 protein overexpression was observed in the nuclei of tumoral cells. Cases were divided into two groups according to their immunoreactivity intensity and percentage of p53 positive tumor cells.
Li et al.  stated that p53 dysfunction in NPCs may be involved in the regulation of NPC cell growth. Gulley et al.  evaluated the association between EBV infection and p53 accumulation in NPCs. They found that EBVinfected tumors are more likely to express p53 than are tumors lacking EBV, and they concluded that there is a strong correlation between the presence of EBV and the accumulation p53 in tumor cells.
Masuda et al.  studied p53 and Ki-67 expression in NPCs and they found no association between the Ki-67 LI and clinicopathological parameters, radiosensitivity, distant metastases, or survival of patients with NPCs, suggesting that, in these tumors, the Ki-67 level lacks clinical significance. However, they suggested that the overexpression of p53 is a clinical prognostic factor associated with resistance to treatment with agents that damage DNA in patients with NPCs.
We observed strong positivity for p53 in keratinizing SCCs and weaker staining in undifferentiated cases but the number of our cases is not enough to make a conclusion.
Ki-67 is a nuclear antigen that is expressed in proliferating cells during the G1, S, G2 and M phases of the cell cycle. Its expression is used as a marker cell proliferation. Many studies have confirmed in a variety of human malignant tumors between a high Ki-67 LI and a poor prognosis. However, other studies, in prostate cancer and carcinomas of head and neck have shown no correlation between Ki- 67 index and prognosis .
Genc et al.  also studied p53 and Ki-67 in NPCs. According to them, a high percentage of p53 and Ki-67 expression was associated with the stage and tumor behavior. Yazici et al.  also found similar results with p53.
In our study the Ki67 LI was higher in keratinizing SCCs which have the worst prognosis and it was least in undifferentiated cases which are known to have the best response to therapy.
Although limited number of cases are included in this study, we found correlation between histopathologic subtypes, p53 and Ki-67 expression in NPCs. The Ki-67 LI was higher in cases with high percentage of p53 positive tumor cells.